Byzantine–Bulgarian war of 913–927

The Byzantine–Bulgarian war of 913–927 (Българо–византийска война от 913–927) was fought between the Bulgarian Empire and the Byzantine Empire for more than a decade. Although the war was provoked by the decision of the Byzantine emperor Alexander to discontinue the annual tribute paid to Bulgaria, the military and ideological initiative was held by Simeon I of Bulgaria who demanded to be recognized as Tsar, a title equal to that of the Byzantine emperor, and aimed to conquer Constantinople and the Byzantine Empire.

In 917 the Bulgarian army dealt a crushing defeat on the Byzantines in the battle of Achelous resulting in total Bulgarian military supremacy in the Balkan Peninsula. The Byzantines were defeated again at Katasyrtai in 917 and at Pegae in 922. The Bulgarians captured the important city of Adrianople in Thrace and seized the capital of the theme of Hellas, Thebes deep into southern Greece. After the disaster at Achelous the Byzantine diplomacy incited the Principality of Serbia to attack Bulgaria in the rear to the west but the Serb threat was easily contained. However, in 924 the Serbs managed to ambush and defeat a small army provoking a major retaliatory campaign that ended with the annexation of Serbia in the end of the same year.

Simeon I was aware that he needed naval support to conquer Constantinople and in 922 sent envoys to the Fatimid caliph Ubayd Allah al-Mahdi Billah in Mahdia to negotiate the assistance of the powerful Arab navy. The caliph agreed to sent his own representatives back to Bulgaria to arrange an alliance. However, the envoys were captured en route by the Byzantines near the Calabrian coast. Emperor Romanos I Lekapenos managed to avert a Bulgarian–Arab alliance with generous gifts. By the date of his death, 27 May 927, Simeon I controlled almost all Byzantine possessions in the Balkans but was unable to seize Constantinople.

In 927 both countries were exhausted by the huge military efforts that took heavy toll on the population and economy. Simeon I's successor Peter I negotiated a favourable peace treaty. The Byzantines agreed to recognize him as Emperor of Bulgaria and the Bulgarian Orthodox Church as an independent Patriarchate, as well as to pay an annual tribute. The peace was reinforced with a marriage between Peter I and Romanos I's granddaughter Irene Lekapene. This agreement ushered a period of 40 years of peaceful relations between the two powers, a time of stability and prosperity for both Bulgaria and the Byzantine Empire.

Political background
Soon after his accession to the throne in 893, Simeon I successfully defended Bulgaria's commercial interests, acquired territory between the Black Sea and the Strandzha mountains, and imposed an annual tribute on the Byzantine Empire as a result of the Byzantine–Bulgarian war of 894–896. The outcome of the war confirmed the Bulgarian domination on the Balkans but Simeon I was aware that he needed to consolidate his political, cultural and ideological base in order to fulfil his ultimate goal — to assume the throne in Constantinople. He implemented an ambitious construction programme in Bulgaria's new capital, Preslav, so that the city could rival Constantinople. Simeon I continued the policy of his father, Boris I (r. 852–889), of establishing and spreading Bulgarian culture, turning the country into the literary and spiritual centre of Slavic Europe. The Preslav Literary School and Ohrid Literary School, founded under Boris I, reached their apogee during the reign of his successor. It was at this time that the Cyrillic alphabet was invented, most likely by the Bulgarian scholar Clement of Ohrid. The Magyar devastation of the country's north-eastern regions during the War of 894–896 exposed the vulnerability of Bulgaria's borders to foreign intervention under the influence of the Byzantine diplomacy. As soon as the peace with Byzantium had been signed, Simeon I sought to secure the Bulgarian positions in the western Balkans. After the death of prince Mutimir (r. 850–891), several members of the ruling dynasty fought over the throne of the Principality of Serbia. In 892 Petar Gojniković established himself as a prince. In 897 Simeon I agreed to recognize Petar and put him under his protection, resulting in a twenty-year period of peace and stability to the west. However, Petar was not content with his subordinate position and sought ways to achieve independence.

The internal situation of the Byzantine Empire in the beginning of the 10th century was interpreted by Simeon I as a sign of weakness. There was an attempt to murder emperor Leo VI the Wise (r. 886–912) in 903 and a rebellion of the commander of the Eastern army Andronikos Doukas in 905. The situation deteriorated further as the emperor entered in feud with the Ecumenical Patriarch Nicholas Mystikos over his fourth marriage to his mistress Zoe Karbonopsina, and had the patriarch deposed.

Crisis of 904
In the beginning of the 10th century the Arabs completed their conquest of Sicily and from 902 began attacking Byzantine shipping and towns in the Aegean Sea. In 904 they sacked the empire's second largest city, Thessalonica, taking 22,000 captives and leaving the city virtually empty. Simeon I took steps to exploit that opportunity and the Bulgarian army appeared in the vicinity of the deserted city. By securing and settling Thessalonica, the Bulgarians would have gained an important port on the Aegean Sea and cemented their hold on the western Balkans, creating a permanent threat to Constantinople. Aware of the danger, the Byzantines sent the experienced diplomat Leo Choirosphaktes to negotiate a solution. The course of the negotiations is unknown — in a surviving letter to emperor Leo VI the Wise Choirosphaktes boasted that he had "convinced" the Bulgarians not to take the city but did not mention more details. However, an inscription found near the village of Narash testifies that since 904 the border between the two countries ran only 20 km to the north of Thessalonica. As a result of the negotiations Bulgaria secured the gains in Macedonia acquired during the reign of Khan Presian I (r. 836–852) and expanded its territory further south, taking possession of most of the region. The western section of the Byzantine–Bulgarian border ran from the Falakro mountain through the town of Serres which lay on the Byzantine side, then turned south-west to Narash, crossed the river Vardar at the modern village of Axiohori, ran through Mount Paiko, passed east of Edessa through Vermio and Askio mountains, crossed the river Haliacmon south of the town of Kostur, which lay in Bulgaria, ran through the Gramos mountains, then followed the river Aoös until its confluence with the river Drino and finally turn west, reaching the Adriatic Sea at the town of Himarë.

Beginning of the war and Simeon I's coronation
In 912 Leo VI died and was succeeded by his brother Alexander, who set about reversing many of Leo VI's policies and reinstated Nicholas Mystikos as patriarch. As the diplomatic protocol of the time prescribed, Simeon I sent emissaries to confirm the peace in late 912 or early 913. According to the Byzantine chronicler Theophanes Continuatus Simeon I informed that "he would honour the peace if he was to be treated with kindness and respect, as it was under emperor Leo. However, Alexander, overwhelmed by madness and folly, ignominiously dismissed the envoys, made threats to Simeon and thought he would intimidate him. The peace was broken and Simeon decided to raise arms against the Christians [the Byzantines]." The Bulgarian ruler, who was seeking a casus belli to claim the imperial title, took the opportunity to wage war. Unlike his predecessors, Simeon I's ultimate ambition was to assume the throne of Constantinople as a Roman emperor, creating a joint Bulgarian–Roman state. The historian John Fine argues that the provocative policy of Alexander did little to influence Simeon I's decision, as he had already planned an invasion, taking into account that on the Byzantine throne sat an unpopular, inexperienced and possibly alcoholic person, whose successor, Constantine VII, was a sickly little boy, considered by many to be illegitimate. While Bulgaria was preparing for war, on 6 June 913 Alexander died, leaving Constantinople in chaos with an under-aged emperor under the regency of patriarch Nicholas Mystikos.

The first steps of the regency were to attempt to divert Simeon I's attack. Nicholas Mystikos sent a letter which, while praising the wisdom of Simeon, accused him of attacking an "orphan child" (i.e. Constantine VII) who had done nothing to insult him, but his efforts were in vain. In the end of July 913 the Bulgarian monarch launched a campaign at the head of a large army and in August he reached Constantinople unopposed. The head of the Byzantine chancery, Theodore Daphnopates, wrote about the campaign 15 years later: "There was an earthquake, felt even by those who lived beyond the Pillars of Hercules". The Bulgarians besieged the city and constructed ditches from the Golden Horn to the Golden Gate at the Marmara Sea. Since Simeon I had studied in the University of Constantinople and was aware that the city was impregnable to a land attack without maritime support, those actions were a demonstration of power, not an attempt to assault the city. Soon the siege was lifted and kavhan (first minister) Theodore Sigritsa was sent to offer peace. Simeon I had two demands — to be crowned emperor of the Bulgarians and to betroth his daughter to Constantine VII, thus becoming father-in-law and guardian of the infant emperor.

After negotiations between Theodore Sigritsa and the regency, a feast was organised in honour of Simeon I's two sons in the Palace of Blachernae presided over personally by Constantine VII. Patriarch Nicholas Mystikos went to the Bulgarian camp to meet the Bulgarian ruler in the midst of his entourage. Simeon I prostrated himself before the Patriarch, who instead of an imperial crown placed upon Simeon I's head his own patriarchal crown. The Byzantine chronicles, who were hostile to Simeon, had presented the ceremony as a sham, but modern historians, such as John Fine, Mark Whittow and George Ostrogorsky, argue that Simeon was too experienced to be fooled and he was indeed crowned Emperor of the Bulgarians (in Bulgarian, Tsar). The sources suggest that Nicholas Mystikos also agreed to Simeon's second condition which could have paved his route to become co-emperor and eventually emperor of the Romans. Having achieved his goal, Simeon I returned to Preslav in triumph, after he and his sons were honoured with many gifts. To mark this achievement Simeon changed his seals to read "Simeon, peacemaking emperor, [may you reign for] many years".

Battle of Achelous
The agreement concluded in August 913 proved to be short-lived. Two months later Constantine VII's mother Zoe Karbonopsina was allowed to return to Constantinople from exile. In February 914 she overthrew the regency of Nicholas Mystikos in a palace coup. She was reluctantly proclaimed empress by Mystikos, who retained his post as a Patriarch. Her first order was to revoke all concessions given to the Bulgarian monarch by the regency, provoking military retaliation. In the summer of 914 the Bulgarian army invaded the themes of Thrace and Macedonia. Simultaneously, the Bulgarian troops penetrated into the regions of Dyrrhachium and Thessalonica to the west. Thrace's largest and most important city, Adrianople, was besieged and captured in September and the local population recognized Simeon I as its ruler. However, the Byzantines promptly regained the city in return of a huge ransom.

To deal with the Bulgarian threat for good, the Byzantines took measures to end the conflict with the Abbasid Caliphate in the east and attempted to create a wide anti-Bulgarian coalition. Two envoys were sent to Baghdad and in June 917 they managed to secure peace with caliph al-Muqtadir. The strategos of Dyrrhachium Leo Rhabdouchos was instructed to negotiate with the Serbian prince Petar Gojniković, who was a Bulgarian vassal but was willing to renounce Bulgarian suzerainty. However, the court in Preslav was warned about the negotiations by prince Michael of Zahumlje, a loyal ally of Bulgaria, and Simeon I was able to prevent an immediate Serb attack. The Byzantine attempts to approach the Magyars were also successfully countered by Bulgarian diplomacy. The general John Bogas was sent with rich gifts to the Pechenegs, who inhabited the steppes to the north-east of Bulgaria. The Bulgarians had already established strong connection with the Pechenegs, including through marriages, and Bogas' mission proved to be a hard one. He did manage to convince some tribes to send aid but eventually the Byzantine navy refused to transport them to the south of the Danube river, probably as a result of the jealousy that existed between Bogas and the ambitious admiral Romanos Lekapenos.

The Byzantines were forced to fight alone, but the peace with the Arabs allowed them amass their whole army, including the troops stationed in Asia Minor, under the command of the Domestic of the Schools Leo Phokas the Elder. Before marching to battle the soldiers bowed to "the life-giving True Cross and vowed to die for one another". With his western and northern border secure, Simeon I was also able to muster a large host. The two armies clashed on 20 August 917 near the river Achelous in the vicinity of Anchialus. Initially the Byzantines were successful and the Bulgarians began an orderly retreat but when Leo Phokas lost his horse, confusion spread among the Byzantine troops, who according to the chronicler John Skylitzes had low morale. Simeon I, who was monitoring the battlefield from the nearby heights, ordered a counter-attack and personally led the Bulgarian cavalry. The Byzantine ranks broke and in the words of Theophanes Continuatus "a bloodshed occurred, that had not happened for centuries". Almost the whole Byzantine army was annihilated and only a few, including Leo Phokas, managed to reach the port of Messembria and flee to safety on ships.

Once again, Nicholas Mystikos was summoned in an attempt to stop the Bulgarian onslaught. In a letter to Simeon I, the patriarch insisted that the purpose of the Byzantine attack had been not to destroy Bulgaria but to force Simeon to evacuate his troops from the regions of Thessalonica and Dyrrhachium. Yet, he admitted that this was not an excuse for the Byzantine invasion and pleaded that as a good Christian Simeon should forgive his fellow Christians. The efforts of Nicholas Mystikos were in vain and the Bulgarian army penetrated deep into Byzantine territory. Leo Phokas gathered another host but the Byzantines were heavily defeated in the battle of Katasyrtai just outside Constantinople in a night combat.

Campaigns against the Serbs
Following the victories in 917 the way to Constantinople lay open. However, Simeon I had to deal with the Serbian prince Petar Gojniković, who had responded positively to the Byzantine proposal for an anti-Bulgarian coalition. An army was dispatched under the command of Theodore Sigritsa and Marmais. The two persuaded Petar Gojniković to meet them, seized him and sent his to Preslav, where he died in prison. The Bulgarians replaced Petar with Pavle Branović, a grandson of prince Mutimir, who had long lived in Preslav. Thus, Serbia was turned into a puppet state until 921.

In an attempt to bring Serbia under their control, in 920 the Byzantines sent Zaharija Pribislavljević, another of Mutimir's grandsons, to challenge the rule of Pavle. Zaharija was either captured by the Bulgarians en route or by Pavle, who had him duly delivered to Simeon I. In either way, Zaharija ended up in Preslav. Despite the setback, the Byzantines persisted and eventually bribed Pavle to switch sides after lashing much gold on him. In response, in 921 Simeon I sent a Bulgarian army headed by Zaharija. The Bulgarian intervention was successful, Pavle was easily deposed and once again a Bulgarian candidate was placed on the Serbian throne. This did not last long, because Zaharija was raised in Constantinople where he was heavily influenced by the Byzantines. Soon Zaharija openly declared his loyalty to the Byzantine empire and commenced hostilities against Bulgaria. In 923 or in 924 Simeon I sent a small army led by Thedore Sigritsa and Marmais but they were ambushed and killed. Zaharija sent their heads to Constantinople.

This action provoked a major retaliatory campaign in 924. A large Bulgarian force was dispatched, accompanied by a new candidate, Časlav, who was born in Preslav to a Bulgarian mother. The Bulgarians ravaged the countryside and forced Zaharija to flee to the Kingdom of Croatia. This time, however, the Bulgarians had decided to change the approach towards the Serbs. They summoned all Serbian župans to pay homage to Časlav, had them arrested and taken to Preslav. Serbia was annexed as a Bulgarian province, expanding the country's border to Croatia, which was at its apogee and proved to be a dangerous neighbour. The annexation was a necessary move since the Serbs had proved to be unreliable allies and Simeon I had grown wary of the inevitable pattern of war, bribery and defection.

Campaigns against the Byzantines (917–922)
With the Serbian threat eliminated and the bulk of the Byzantine army destroyed, in 918 Simeon I personally led a campaign in the Theme of Hellas and penetrated deep to the south, reaching Corinth. The Bulgarians took a lot of captives and forced the population to pay taxes to the Bulgarian state, while many people fled to island of Euboea and the Peloponnese peninsula to seek refuge. The capital of Hellas, Thebes, was seized and its fortifications were destroyed. A noteworthy episode of that campaign was described in the manual on warfare, the Strategikon, of the 11th-century writer Kekaumenos. After fruitlessly besieging a populous city in Hellas, Simeon employed a ruse de guerre by sending brave and resourceful men into the city to discover weaknesses in the defence. They found out that the gates were held high above the ground on hinges. After receiving their report, Simeon sent inside five men with axes who eliminated the guards, broke the hinges and opened the gates to the Bulgarian army. The Bulgarians moved in and took the city without bloodshed.

The military setbacks triggered another change in the Byzantine government. In the spring of 919 the admiral Romanos Lekapenos forced Zoe Karbonopsina back into a monastery and quickly rose to prominence. In April 919 his daughter Helena Lekapene was married to Constantine VII and Lekapenos assumed the title basileopator; in September he was named Caesar, and in December 919 Romanos Lekapenos was crowned senior emperor. This new development infuriated Simeon, who considered Romanos an usurper and felt insulted that a son of an Armenian peasant, had taken his own promised position. The Bulgarian emperor refused the offers to become related with Romanos by a dynastic marriage or to negotiate for peace until he stepped down.

In the autumn of 920 the Bulgarian army campaigned deep into Thrace, reached the Dardanelles and camped on the Gallipoli peninsula on the shore just across the city of Lampsacus in Asia Minor. Those actions brought great concern to the Byzantine court because if successful in securing Lampsacus and Gallipoli, the Bulgarians would have cut Constantinople off from the Aegean Sea. Patriarch Nicholas Mystikos tried to sue for peace and proposed to meet Simeon in Mesembria, but to no avail. In the next year the Bulgarians marched to Katasyrtai near Constantinople and the Byzantines retaliated with a campaign to the town of Aquae Calidae, near modern Burgas. The Byzantine commander Pothos Argyros sent a detachment under Michael, son of Moroleon, to monitor the movements of the Bulgarians. Michael's troops were ambushed and although they inflicted significant casualties on the Bulgarians, the Byzantines were defeated and Michael was wounded and had to flee to Constantinople, where he died. A large Bulgarian force was sent south led by kavhan Theodore Sigritsa. They crossed the Strandzha mountains and ravaged the countryside around Constantinople, threatening the palaces around the Golden Horn. The Byzantines summoned a large army, including troops from the city garrison, the imperial guard and sailors from the navy, commanded by Pothos Argyros and admiral Alexios Mosele. In March 921 the opposing forces clashed in the battle of Pegae and the Byzantines were completely defeated. Pothos Argyros barely escaped and Alexios Mosele drowned while attempting to board a ship. In 922 the Bulgarians captured the town of Vizye and burned the palaces of empress Theodora near the Byzantine capital. Romanos I tried to oppose them by dispatching troops under Saktikios. Saktikios attacked the Bulgarian camp while most soldiers were scattered to gather supplies but when the main Bulgarian forces were informed for the attack, they engaged and defeated the Byzantines, whose commander died from his wounds during the next night.

Attempts for a Bulgarian–Arab alliance
By 922 the Bulgarians controlled almost the whole Balkan peninsula but Simeon I's main objective remained out of his reach. The Bulgarian monarch was aware that he needed a navy to conquer Constantinople. Simeon I decided to turn to Abdullah al-Mahdi Billah (r. 909–934), founder and caliph of the Fatimid Caliphate. He ruled most of North Africa and posed a constant threat to the Byzantine possessions in South Italy. Although both sides had concluded a peace treaty in 914, since 918 the Fatimids had renewed their attacks on the Italian coast. In 922 the Bulgarians clandestinely sent envoys via Zachlumia, the state of their ally Michael, to the caliph's capital al-Mahdiyyah on the Tunisian coast. Simeon I suggested a joined attack on Constantinople with the Bulgarians providing a large land army, and the Arabs — a navy. It was proposed that all spoils would be divided equally, the Bulgarians would keep Constantinople and the Fatimids would gain the Byzantine territories in Sicily and South Italy.

Abdullah al-Mahdi Billah accepted the proposal and sent back his own emissaries to conclude the agreement. On the way home the ship was captured by the Byzantines near the Calabrian coast and the envoys of both countries were sent to Constantinople. When Romanos I learned about the secret negotiations, the Bulgarians were imprisoned, while the Arab envoys were allowed to return to Al-Mahdiyyah with rich gifts for the caliph. The Byzantines then sent their own embassy to North Africa to outbid Simeon I and eventually the Fatimids agreed not to aid Bulgaria. Another attempt of Simeon I to ally with the Arabs was recorded by the historian al-Masudi in his book Meadows of Gold and Mines of Gems. An Arab expedition from the Abbasid Caliphate under Thamal al-Dulafi landed on the Aegean coast of Thrace and the Bulgarians established contact with them and sent envoys in Tarsus. However, this attempt also failed to produce tangible results.

Later years
After the failure to secure an alliance with the Arabs, in September 923 or 924 Simeon I once again appeared in Byzantine Thrace. The Bulgarians pillaged the outskirts of Constantinople, burned the Church of St. Mary of the Spring and set camp at the walls of Constantinople. Simeon I demanded a meeting with Romanos I in order to establish a temporary truce to deal with the Serbian threat. The Byzantines, eager to cease the hostilities, agreed. Prior to the meeting, the Bulgarians took precautions and carefully inspected the specially prepared platform — they still remembered the failed Byzantine attempt to assassinate Khan Krum (r. 803–814) during negotiations at the same place a century earlier, in 813.

Romanos I arrived first; Simeon I appeared on a horse surrounded by elite soldiers who shouted in Greek "Glory to Simeon, the Emperor". According to the Byzantine chronicles, after the two monarchs had kissed, Romanos I demanded that Simeon I stop spilling Christian blood in an unnecessary war and delivered a small sermon on the ageing Bulgarian ruler about how he could face God with all that blood on his hands. Simeon I had nothing to respond. However, historian Mark Whittow notes that those accounts were nothing but official Byzantine wishful thinking, composed after the event. The only hint of what really happened was an allegoric story that in the moment the meeting concluded, two eagles were seen flying high in the sky, then they engaged and immediately separated, one headed northwards to Thrace, the other flew to Constantinople. This was seen as a bad omen representing the fates of the two rulers. The portent of two eagles is a rhetorical implication that in the meeting Romanos I recognized Simeon I's imperial title and his equal status to the emperor in Constantinople. However, Romanos I never ratified the agreement in Simeon I's lifetime and the contradictions between the two sides remained unsolved. In a correspondence dated from 925 the Byzantine emperor criticized Simeon I for calling himself "Emperor of the Bulgarians and the Romans" and demanded the return of the conquered fortresses in Thrace.

In 926 the Bulgarians sent an army to invade the Kingdom of Croatia in order to secure their rear for a new offensive on Constantinople. Simeon I saw the Croatian state as a threat because king Tomislav (r. 910–928) was a Byzantine ally and harboured his enemies. The Bulgarians marched into Croatian territory but suffered a complete defeat at the hands of the Croats. However, peace was quickly restored through Papal mediation. Since Simeon I persisted in the preparation for an assault on the Byzantine capital, it was evident that the Bulgarian losses were not significant because only a small portion of the whole army was sent to fight the Croats. The Bulgarian monarch seemed secure that king Tomislav would honour the peace. However, like his great predecessor Krum, Simeon I died in the midst of the preparations for an attack on Constantinople on 27 May 927, aged sixty–three.

Peace treaty
Simeon I was succeeded by his second son Peter I (r. 927–969). In the beginning of Peter I's reign the most influential person in the court was his maternal uncle George Sursuvul who served at first as a regent for the young monarch. Upon his accession to the throne, Peter I and George Sursuvul launched a campaign in Byzantine Thrace, razing the fortresses in the region that had been held until then by the Bulgarians. The raid was meant as a demonstration of power and from a position of strength the Bulgarians proposed peace. Both sides sent delegations in Mesembria to discuss the preliminary terms. Then the negotiations continued in Constantinople until the final provisions were reached. In November 927 Peter I himself arrived in the Byzantine capital and was received personally by Romanos I. In the Palace of Blachernae the two sides signed a peace treaty, sealed by a marriage between the Bulgarian monarch and the granddaughter of Romanos I, Maria Lekapene. On that occasion Maria was renamed Irene, meaning "peace". On 8 October 927 Peter I and Irene were married in a solemn ceremony in the Church of St. Mary of the Spring — the same church that Simeon I had destroyed a few years earlier and that had been rebuilt. By the treaty the Byzantines officially recognized the imperial title of the Bulgarian monarchs but insisted on the formula that the Emperor of the Bulgarians was a "spiritual son" of the Byzantine Emperor. Despite the wording, the title of the Bulgarian rulers equalled that of their Byzantine counterparts. The Bulgarian Orthodox Church was also recognized as an independent Patriarchate, thus becoming the fifth autocephalous Eastern Orthodox Church after the patriarchates of Constantinople, Alexandria, Antioch and Jerusalem and the first national Orthodox Church. The treaty further stipulated the exchange of prisoners and that the Byzantines would pay annual tribute to the Bulgarian Empire. The treaty restored the border approximately along the lines agreed in 904 — the Bulgarians returned most Simeon I's conquests in Thrace, Thessaly and Hellas and retained firm control over most of Macedonia and the larger part of Epirus. Thus, Peter I succeeded to obtain all of his father's goals, except for taking of Constantinople.

Aftermath
During the first years of his reign Peter I faced revolts by two of his three brothers, John in 928 and Michael in 930, but both were quelled. During most of his subsequent rule until 965, Peter I presided over a Golden Age of the Bulgarian state in a period of political consolidation, economic expansion and cultural activity. A treatise of the contemporary Bulgarian priest and writer Cosmas the Priest describes a wealthy, book-owning and monastery-building Bulgarian elite and the preserved material evidence from Preslav, Kostur and other locations imply a wealthy and settled picture of 10th century Bulgaria. The influence of the landed nobility and the higher clergy increased significantly at the expense of the personal privileges of the peasantry which caused frictions in the society. Cosmas the Priest accused the Bulgarian abbots and bishops of greed, gluttony and neglect towards their flock. In that setting during the reign of Peter I arose Bogomilism — a dualistic heretic sect that in the subsequent decades and centuries spread in the Byzantine Empire, northern Italy and southern France (cf. Cathars). The strategic position of the Bulgarian Empire remained difficult. The country was ringed by aggressive neighbours — the Magyars to the north-west, the Pechenegs and the growing power of Kievan Rus' to the north-east, and the Byzantine Empire to the south, which despite the peace proved an unreliable neighbour.

The peace treaty allowed the Byzantine Empire to concentrate its resources on the declining Abbasid Caliphate to the east. Under the talented general John Kourkouas the Byzantines reversed the course of the Byzantine–Arab wars winning striking victories over the Muslims. By 944 they had raided the cities of Amida, Dara and Nisibis in the middle Euphrates and besieged Edessa. The remarkable Byzantine successes continued under Nikephoros Phokas, who ruled as emperor between 963 and 969, with the reconquest of Crete in 961 and the recovery of some territories in Asia Minor. The growing Byzantine confidence and power urged Nikephoros Phokas to refuse the payment of the annual tribute to Bulgaria in 965. This resulted in a Rus' invasion of Bulgaria in 968–971 which led to a temporary collapse of the Bulgarian state and a bitter 50-year Byzantine-Bulgarian war until the conquest of the Bulgarian Empire by the Byzantines in 1018.