History of Isles of Scilly

until relatively recent times the islands were much larger and perhaps joined together into one island named Ennor. Rising sea levels flooded the central plain around 400–500 CE, forming the current islands. There were ten islands in Roman times, but some of these, including Tean, are now under the sea. Ennor was the largest island and its name is a contraction of En Noer (Moer - mutated to Noer), meaning the 'great island'.

Evidence for the older large island includes:

A description in Roman times describes Scilly as "Scillonia insula" in the singular, indicating either a single island or an island much bigger than any of the others.

Remains of a prehistoric farm have been found on Nornour, which is now a small rocky skerry far too small for farming.

At certain low tides the sea becomes shallow enough for people to walk between some of the islands. This is possibly one of the sources for stories of drowned lands, e.g. Lyonesse.

Ancient field walls are visible below the high tide line off some of the islands (e.g. Samson).

Some of the Cornish language place names also appear to reflect past shorelines, and former land areas.

The whole of southern England has been steadily sinking in opposition to post-glacial rebound in Scotland: this has caused the rias (drowned river valleys) on the southern Cornish coast, e.g. River Fal and the Tamar Estuary.

Offshore, midway between Land's End and the Isles of Scilly, is the supposed location of the mythical lost land of Lyonesse, referred to in Arthurian literature. This may be a folk memory of inundated lands, but this legend is also common among the Brythonic peoples;