Callixtus II

Pope Callixtus II (c. 1065 – 13 December 1124), born Guy of Burgundy, was Pope from 1119 to his death.

During his papacy, Callixtus created a small channel through the sealed Porta Metronia for the Acqua Mariana, a river whose stagnant waters would later cause an outbreak in 1601.

Reference

 * Assassin's Creed: Brotherhood