Derry originally started out as a monastery in the 6th century said to be founded by Saint Columba (or Colmcille). Derry is one of the longest inhabited places in Ireland, there is evidence that people had been living in the area for thousands of years before the monastery was built. It was founded on the hill of Doire. It was originally a small island on the river Foyle, but over time the western side of the island dried out and became a swampy, boggy area, which eventually came to be called the Bogside, one of the most well-known parts of the city. It was a small monastery for many years until the late middle ages when it was expanded into an Augustinian monastery. The church of the monastery survived up to the 17th century and was used by the London colonists.
Though the Vikings reached the area and sailed up the loughs and rivers, the monastery managed to escape the worst effects of their raids. During the 12th and 13th centuries, Derry thrived and prospered under the patronage of the Mac Lochlainn dynasty. The monastery and its school flourished and prestigious buildings were erected. Eventually the Mac Lochlainns declined, and Derry lost importance.