Maasi is best known for Maasilinna Castle (German: Soneburg), which in Medieval times served as the centre of Eastern Saaremaa and Muhu. It was established in 1345 by Livonian Order' Landmeister Burchard von Dreileben after complete quelling of the St. George's Night Uprising. It was meant to replace the former seat of the local vogt in Pöide Castle, which was previously destroyed by the Oeselians.