Before 500 BC, Miletus was the greatest Greek city in the east. It was the natural outlet for products from the interior of Anatolia and had a considerable wool trade with Sybaris, in southern Italy. By the mid-5th century the city had been weakened and impoverished by internal divisions, and in 442 it was defeated in war by neighbouring Samos.Its fortunes soon revived, however, and the Milesians set about rebuilding their city on a new grid plan of the type invented in this period by Hippodamus of Miletus. Miletus retained its commercial importance and received special attention from the Roman emperors Augustus and Trajan. By the 6th century AD, however, its two harbours had silted up, and it was eventually abandoned.The ruins occupy the former peninsula crowned by the hill of Kalabak Tepe. The total area of the archaic city is unknown, but Hellenistic town walls and foundations have been uncovered. There also are extensive remains of the classical city from the 5th century BC to Roman imperial times. The Greco-Roman theatre and its adjoining Byzantine castle are the most visible of the site's ruins. (Enc. Britt.)
I have been informed this is the Harbour Monument.