First Sacred War

The First Sacred War (595 BC-585 BC), or Cirraean war, was fought between the Amphictyonic League of Delphi and the city of Kirrha. The conflict arose due to Kirrha's frequent robbery and mistreatment of pilgrims going to Delphi and their encroachments upon Delphic land. The war resulted in the defeat and destruction of Kirrha. The war is notable for the use of chemical warfare at the Siege of Kirrha, in the form of hellebore being used to poison the city's water supply.

Justifications of war
In ancient Greece, Kirrha was a heavily fortified city which controlled access to Delphi from the Corinthian Gulf. Kirrha took advantage of its location to rob and mistreat pilgrims to the Delphic Oracle, to tax Delphi, and to steal land from Delphi, land considered sacred to Apollo. This behavior prompted many of the other Greek city-states to form the Amphictionic League, a military alliance dedicated to protecting Delphi, c. 600 BC. The League consulted the oracle for advice on dealing with Kirrha, and the reply was a call for total war. The members of the league vowed to completely destroy Kirrha and ravage the surrounding areas. To this they added a curse in the name of Apollo: that the soil should bring forth no crops, that the children of the women and livestock should be deformed, and that the entire ethnic group that inhabited the city should be eradicated.

Siege of Kirrha
The leader of the attack was the Tyrant Cleisthenes of Sicyon, who used his powerful navy to blockade the city's port before using an allied Amphictionic army to besiege Kirrha. What transpired after this is a matter of debate. The earliest, and therefore probably most reliable, account is that of the medical writer Thessalos. He wrote, in the 5th century BC, that the attackers discovered a secret water-pipe leading into the city after it was broken by a horse's hoof. An asclepiad named Nebros advised the allies to poison the water with hellebore. The hellebore soon rendered the defenders so weak with diarrhea that they were unable to continue resisting the assault. Kirrha was captured and the entire population was slaughtered. Nebros was an ancestor of Hippocrates, so this story has caused many to wonder whether it might not have been guilt over his ancestor's use of poison that drove Hippocrates to establish the Hippocratic Oath.

Later historians told different stories. According to Frontinus, who wrote in the 1st century AD, that after discovering the pipe, the Amphictionic League cut it, leading to great thirst within the city. After a while, they restored the pipe, allowing water to flow into the city. The desperate Kirrhans immediately began drinking the water, unaware that Kleisthenes had poisoned it with hellebore. According to Polyaenus, a writer of the 2nd century, after the pipe was discovered, the attackers added the hellebore to the spring from which the water came, without ever actually depriving the Kirrhans of water. Polyaenus also gave credit for the strategy not to Kleisthenes but to General Eurylochus, who he claimed advised his allies to gather a large amount of hellebore from Anticyra, where it was abundant. The stories of Frontinus and Polyaenus both have the same result as Thessalos's tale: the defeat of Kirrha.

The last major historian to advance a new story of the siege was Pausanias, who was active in the 2nd century. In his version of events, Solon of Athens diverted the course of the River Pleistos so that it didn't run through Kirrha. Solon had hoped to thus defeat the Kirrhans by thirst, but the enemy was able to get enough water from their wells and rainwater collection. Solon then added a great quantity of hellebore to the water of the Pleistos and let it flow into Kirrha. The poisoning then allowed the allies to destroy the city.