Thessaloníki or Salonika, which is a city and port in northeastern Greece, and also one of the largest cities of Greece and the chief port and commercial center of Macedonia in Greece, was founded in 315 B.C. The city is the capital and sea port of Thessalonika . It is also the seat of the Aristotle University of Thessaloníki (1925). It was one of the first bases for the spread of Christianity. Among its Christian monuments are fine churches which was constructed over a long period, from the 4th to the 15th century, they constitute a diachronic typological series, which had considerable influence in the Byzantine world. The mosaics of the rotunda, St Demetrius and St David are among the great masterpieces of early Christian art.