Ancient Eresos—birthplace of the philosopher and botanist, Theophrastus, and (by general consensus) of Sappho—was by the sea, at the eastern end of the shore. The inland Eresos of today, on a steep hill at the northern extremity of the cultivated plain above the valley of one of the torrents, was founded in the early Middle Ages when it was necessary to move inland as a refuge against coastal piracy. The town is large, and its four-square stone houses, with low tiled roofs typical of the Levant coast, spread widely onto the plateau to the north of the centre.
At Skala Eresou, which looks onto one the island's most attractive beaches, what remains to be seen of Ancient Eresos lies around the conical hill of Vigla, mentioned by Strabo, at the bay's eastern end. It overlooks a small harbour where beside the modern jetty can be seen the remains of the ancient artificial mole just below water-level. Visible from here, looking back at the eastern slope of the hill, can be seen the remains (rectangular) of a corner bastion constructed in Byzantine masonry, and behind (circular) a Genoese tower of the late 14th century; while below at various points on the lower slopes are small runs of Classical walling, beautifully constructed from blocks of trachytic stone in interlocking polygonal ‘Lesbian' masonry. The blocks appear to have been hewn and shaped with a flat instrument, more like a very broad chisel than a pick. This was part of an enceinte with gates and towers (estimated at 1km in length by the 19th century archaeologist, Koldewey). It was later extended to the south in Hellenistic times with walls constructed in isodomic masonry. Little remains on the surface.
Info: McGilchrist's Greek Islands
(From McGilchrist’s Greek Islands, © Nigel McGilchrist 2010, excerpted with his gracious permission. Click for the books)