Monemvasia was once on the Peloponnese mainland. Then an earthquake turned it into an island. It is now joined to the mainland by a narrow causeway that limits access, originally for reasons of defense. The tall, flat isle is completely honeycombed with nooks and grottoes, narrow alleys and rock-carved rooms. Clearly it was a formidable redoubt in times of attack, and earned its nickname the Gibraltar of the East. The upper town, long uninhabited, has narrow pathways leading to the Byzantine Aghia Sophia church, and remains of the medieval fortress and walls. In the lower town, look for the bell tower that leads you to Elkomenos Square, with its namesake medieval Elkomenos Christos church and a small museum.