The caste of Agia Mavra is located at the entrance of the island. It is one of the most imposing medieval buildings of Greece, representing the fortification art of this period.It was built around 1300 from a Frank leader, Ioannis Orsini, when he took Lefkada as a wedding gift for his wedding with the daughter of Epirus Bishop Nikiforos A.
The castle was protecting the capital of the island, as the most important defensive armoring against Pirates and other enemies, from the first decade of 14th century since 1684. In 1487, it was overtaken by Turks, who built a large arch shaped bridge with 360 rooms, which crossed the lagoon from the coast to Kalkani, resting the pipes of a water tower. This project was destroyed by the earthquakes. Some ruins are still preserved in the lagoon.