The remains of two Churches are situated in the Eastern part of the Polače bay, on the Island of Mljet. The Double Churches (the Northern and the Southern one) were built in the 5th century. The Northern one was expanded probably in the 11th century and is preserved up to 3m in height because it was in use in the Middle Ages. The Southern basilica remained only in its foundations.
Two single nave basilicas were built in the 5th (the Southern one has rectangular apse on the outside and a semicircular apse on the inside). A memorial was added to the South of the Double basilica.
In the early Middle Ages, lesenes were added to the Northern basilica in order to change the wooden into a barrel vaulted structure. At the same time, a vestibule was added to its West side. The walling of the Southern portal, between the two early Christian buildings, proves that since then the Southern part of the complex of Double basilicas was no longer in function.
The church space shaped in this way is known in the pre Romanesque architecture of Dalmatia