Ephesus is one of the largest and best-preserved Roman cities anywhere — at its peak under Augustus, around the time of Christ, it had a population of about 250,000, making it the second-largest city in the empire after Rome itself. The site you visit is essentially a long downhill main street: Curetes Street, paved in marble, lined with the remains of the city's civic buildings, the great public latrines, the Temple of Hadrian, and ending with the photogenic two-storey façade of the Library of Celsus.
Beyond the library a road branches to the 25,000-seat theatre and the line of the old harbour. The Terrace Houses — a separate enclosed enclosure on the south side of Curetes Street, requiring an extra ticket — preserve the painted walls and mosaic floors of seven Roman houses dug into the hillside, and are worth every lira of the extra cost. Allow at least three hours; come early or late to avoid both heat and cruise-ship groups. The South Gate is the better entrance — you walk downhill instead of up.