Sligo Bay is an ancient natural harbour, being known to Greek, Phoenician and Roman traders as the area is thought to be the location marked as the city of Nagnata on Claudius Ptolemy's 2nd century AD co-ordinate map of the world. During the early medieval period, the site of Sligo was eclipsed by the importance of the great monastery founded by Columcille 5 miles to the north at Drumcliff. By the 12th century, there was a bridge and small settlement in existence at the site of the present town.