This is one of the best preserved fortifications of antiquity in the Aegean. The wall is built with large blocks of volcanic black stone and the average width is between 3.50 and 3.80 meters.
The inscription engraved on the north gate states the width of the public area outside the fortifications that had to remain free in case it had to be used for defensive purposes. The inscription dates back to the third quarter of the 4th century BC.
The preserved length of wall on the south is 230 meters, while on the east it is 80 meters. Also, there are rectangular towers, six of which are preserved on the south side and two on the east. The only surviving gate of the wall is located on the southeast and it is 2.10 meters wide. Nowadays it is preserved intact and it is covered by oblong stone plinths which are 3 meters long.
The cornered tower of the wall opposite the gate is 8.50 meters long and a 9 meters wide. The rest of the towers probably had the same dimensions, too. However, the fifth tower is built in a different way and it seems to be a later addition to the already existing tower that might have collapsed. The masonry of the tower, which is often found in fortifications in the Aegean and Asia Minor coast, proves that it was built in the late 4th or early 3rd century BC.
The wall surrounded the ancient city of Nisyros. Within the wall there are the ruins of an early Christian basilica.
The site is open to visitors. Free admission.