In 751 the Lombard King Aistulf conquered most of the Exarchate of Ravenna, leaving Venice a lonely and increasingly autonomous Byzantine outpost. During this period, the seat of the local Byzantine governor (the "duke/dux", later "doge"), was situated in Malamocco. Settlement on the islands in the lagoon probably increased with the Lombard conquest of other Byzantine territories, as refugees sought asylum there. In 775/6 the episcopal seat of Olivolo (San Pietro di Castello; Helipolis) was created. During the reign of duke Agnello Particiaco (811–827) the ducal seat moved from Malamocco to the highly protected Rialto, the current location of Venice. The monastery of St Zachary and the first ducal palace and basilica of St. Mark, as well as a walled defense (civitatis murus) between Olivolo and Rialto, were subsequently built here.