Mole (architecture)

A mole is a massive structure, usually of stone, used as a pier, breakwater, or a causeway between places separated by water. The word comes from Middle French mole, ultimately from Latin mōlēs, meaning a large mass, especially of rock, and it has the same root as molecule. A mole may have a wooden structure built on top of it that resembles a wooden pier. The defining feature of a mole, however, is that water cannot freely flow underneath it, unlike a veritable pier. The oldest known mole is at Wadi al-Jarf, an ancient Egyptian harbor complex on the Red Sea.

San Francisco Bay Area
Historically, the term "mole" was used in the San Francisco Bay Area in California to refer to the combined structure of a causeway and wooden pier or trestle extending out from the eastern shore and utilized by various railroads, such as the Key System, Southern Pacific Railroad (two), and Western Pacific Railroad. By extending the tracks the railroads could get beyond the shallow mud flats and reach the deeper waters of the Bay that could be navigated by ferries. None of the four Bay Area moles survive today, although the causeway portions of each were incorporated into the filling in of large tracts of marshland for harbor and industrial development.

WW2 Dunkirk evacuation
The two concrete moles protecting the outer harbour at Dunkirk played a significant part in the evacuation of British and French troops during World War II in May/June 1940. The harbour had been made unusable by German bombing and it was clear that troops were not going to be taken directly off the beaches fast enough. Naval captain W. G. Tennant had been placed ashore to take charge of the navy shore parties and organise the evacuation. Tennant had what proved to be the highly successful idea of using the East Mole to take off troops. The moles had never been designed to dock ships, but despite this, the majority of troops rescued from Dunkirk were taken off in this way.

Stone quaysides
Stone quaysides are sometimes called moles. A well-known example is the Molo in Venice. It is the site of the Doge's Palace and two pillars which form a gateway to the sea. It has been depicted numerous times by artists such as Canaletto.