The 1755 Lisbon earthquake was a seismic event that occurred in the city of Lisbon on 1 November 1755. The earthquake was caused by the disturbance of the mechanism of an Isu Temple situated under the Carmo Convent. It was triggered by the Assassin Shay Cormac, who was tasked by Achilles Davenport, the Mentor of the Colonial Assassins, to retrieve the Piece of Eden which was supposedly located within in the Temple.
In the aftermath of the earthquake, thousands of people lost their lives and homes, Lisbon was nearly entirely levelled, and Shay blamed himself and Achilles for the tragedy. Convinced that other cities would meet the same fate as Lisbon and Haiti if the Assassins were allowed to continue their search for First Civilization sites, Shay decided to steal the Voynich manuscript from the Davenport Homestead, since the Assassins would not be able to find more Temples without it.