Isles of Scilly: History
=== Early history ===
The islands may correspond to the Cassiterides ("Tin Isles"), believed by some to have been visited by the Phoenicians and mentioned by the Greeks. While Cornwall is an ancient tin-mining region, there is no evidence of this having taken place substantially on the islands.
During the Late Roman Empire, the islands may have been a place of exile. At least one person, one Tiberianus from Hispania, is known to have been condemned c. 385 to banishment on the isles, as well as the bishop Instantius, as part of the prosecution of the Priscillianists.
The isles were part of the Brittonic Celtic kingdom of Dumnonia. In the later Sub-Roman period, c. 7th century AD, the remaining Britons were split into three separate regions: the West (Cornwall), Wales and Cumbria–Ystrad Clyd (Strathclyde). The isles may have been a part of these polities until a short-lived conquest, by the English, in the 10th century was cut short by the Norman Conquest.
It is likely that, until relatively recent times, the islands were much larger, and perhaps conjoined into one island named Ennor. Rising sea levels flooded the central plain around 400–500 AD, forming the current 55 islands and islets (if an island is defined as "land surrounded by water at high tide and supporting land vegetation"). The word Ennor is a contraction of the Old Cornish En Noer (Doer, mutated to Noer), meaning 'the land' or 'the great island'.
Evidence for the older, large island includes:
A description, written during Ancient Roman times, designates Scilly "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 (now a small, rocky skerry far too small for farming). There once was an Iron Age British community here that continued into Roman times. This community was likely formed by immigrants from Brittany—probably the Veneti—who were active in the tin trade that originated in mining activity in Cornwall and Devon.
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 tideline off some of the islands, such as Samson.
Some of the Cornish-language place names also appear to reflect historical 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 (of which Tristan is said to have been a prince). This may be a folk memory of inundated lands, but this legend is also common among the Brythonic peoples; the legend of Ys is a parallel and cognate legend in Brittany, as is that of Cantre'r Gwaelod in Wales. …