Leros is a Greek island and municipality in the Dodecanese in the southern Aegean Sea. It lies 317 km (171 nautical miles) from Athens's port of Piraeus, from which it can be reached by an 11-hour ferry ride (or by a 45-minute flight from Athens). Leros is part of the Kalymnos regional unit. The island has been also called in Italian: Lèro and in Turkish: İleriye.
The island is 74 square kilometres (29 sq mi) and has a coastline of 71 km (44 mi). The municipality includes the populated offshore islands of Pharmakonisi (pop. 74), Levitha (8), and Kinaros (2), as well as several uninhabited islets, and had a 2001 census population of 8,207, although this figure swells to over 15,000 during the summer peak. It is known for its imposing medieval castle of the Knights of Saint John possibly built on a Byzantine fortress.