Among the remains of the Solin buildings, of particular interest is the complex known as Gradina (Hill-Fort), next to the very river and the Roman town’s eastern walls. A church of an unusual ground plan, built over the Roman époque remains, is today situated within a medieval fortress. This was built, according to some authors, by the Split archbishop Ugolino de Mala Branca (1349-1388) to protect the people of Split from the people of Klis. Today, it is in a fortress built during the Venetian-Turkish wars, in the 16th century.
References:Bomarsund fortress and garrison was built in 1832-1854 by Russian Empire to defence Åland Islands against enemies. British and French fleet attacked against it during the Crimean War in 1854. After a week of fighting the British stormed the remaining fort. Anglo-French forces destroyed it totally after battle. In the Treaty of Paris 1856, the entire Åland Islands were demilitarized, which is a status that has been preserved until this day.
Nowadays there are some ruins left and fortress area is open for visitors.