When did purgatory begin to be imagined as a physical place in medieval Europe?

According to the French historian Jacques Le Goff, the conception of purgatory as a physical place emerged in the 12th century. This period saw a rise in otherworld-journey narratives and tales regarding sites such as St. Patrick’s Purgatory, a cave in Ireland believed to be an entrance to the realm.1

While this shift began in the 12th century, the understanding of its location remained fluid for some time; as late as 1220, the monk Caesarius of Heisterbach suggested that purgatory could exist in multiple places simultaneously. The definitive literary depiction of purgatory as a specific, structured location—a seven-story mountain situated at the antipodes to Jerusalem—was later established by Dante Alighieri in his work Purgatorio. These developments occurred alongside the formalization of the doctrine at various church councils, including the Council of Lyon in 1274.12