Although the Isles of Scilly are still part of the ceremonial county of Cornwall, and some services have been combined with those of Cornwall, since 1890 the islands have had a separate local authority. Since the passing of the Isles of Scilly Order 1930, this authority has had the status of a county council and today is known as the Council of the Isles of Scilly. The adjective "Scillonian" is sometimes used for people or things related to the archipelago. The Duchy of Cornwall owns most of the freehold land on the islands. Tourism is a major part of the local economy, along with farming and agriculture. Natural England have designated the Isles of Scilly as National Character Area 158.
The islands may correspond to the Cassiterides (Tin Isles) visited by the Phoenicians and mentioned by the Greeks. However, the archipelago itself does not contain much tin—it may be that the islands were used as a staging post.
It is likely that 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.
Evidence for the older large island includes:
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; the legend of Ys is a parallel and cognate legend in Brittany.
Scilly has been identified as the place of exile of two heretical 4th century bishops, Instantius and Tiberianus, who were followers of Priscillian.
Norse and Norman period
In 995 Olaf Tryggvason became King Olaf I of Norway. Born c. 960, Olaf had raided various European cities and fought in several wars. In 986 he (supposedly) met a Christian seer on the Isles of Scilly. In Snorri Sturluson's Royal Sagas of Norway, it is stated that this seer told him:
Thou wilt become a renowned king, and do celebrated deeds. Many men wilt thou bring to faith and baptism, and both to thy own and others' good; and that thou mayst have no doubt of the truth of this answer, listen to these tokens. When thou comest to thy ships many of thy people will conspire against thee, and then a battle will follow in which many of thy men will fall, and thou wilt be wounded almost to death, and carried upon a shield to thy ship; yet after seven days thou shalt be well of thy wounds, and immediately thou shalt let thyself be baptised.
The legend continues that, as the seer foretold, Olaf was attacked by a group of mutineers upon returning to his ships. As soon as he had recovered from his wounds, he let himself be baptised. He then stopped raiding Christian cities, and lived in England and Ireland. In 995 he used an opportunity to return to Norway. When he arrived, the Haakon Jarl was facing a revolt. Olaf Tryggvason persuaded the rebels to accept him as their king, and Jarl Haakon was murdered by his own slave, while he was hiding from the rebels in a pig sty.
With the Norman Conquest, the Isles of Scilly came more under centralised control. About twenty years later, the Domesday survey was conducted. The islands would have formed part of the "Exeter Domesday" circuit, which included Cornwall, Devon, Dorset, Somerset, and Wiltshire.
In the mid-12th century there was reportedly a Viking attack on the Isles of Scilly, called Syllingar by the Norse, recorded in the Orkneyinga saga— Sweyn Asleifsson "went south, under Ireland, and seized a barge belonging to some monks in Syllingar and plundered it." (Chap LXXIII)
"Maríuhöfn" literally means "Mary's Harbour/Haven". The name does not make it clear if it referred to a harbour on a larger island than today's St Mary's, or a whole island.
It is generally considered that Cornwall, and possibly the Isles of Scilly, came under the dominion of the English Crown late in the reign of Athelstan. In early times one group of islands was in the possession of a confederacy of hermits. King Henry I gave it to the abbey of Tavistock who established a priory on Tresco, which was abolished at the Reformation.
Later Middle Ages and early modern period
At the turn of the 14th century, the Abbot and convent of Tavistock Abbey petitioned the king,
William le Poer, coroner of Scilly, is recorded in 1305 as being worried about the extent of wrecking in the islands, and sending a petition to the King. The names provide a wide variety of origins, e.g. Robert and Henry Sage (English), Richard de Tregenestre (Cornish), Ace de Veldre (French), Davy Gogch (possibly Welsh, or Cornish), and Adam le Fuiz Yaldicz (Spanish?).
It is not known at what point the islands' inhabitants stopped speaking the Cornish language, but the language seems to have gone into decline in Cornwall beginning in the Late Middle Ages; it was still dominant between the islands and Bodmin at the time of the Reformation, but it suffered an accelerated decline thereafter. The islands appear to have lost the old Celtic language before parts of Penwith on the mainland, in contrast to the history of Irish or Scottish Gaelic.
During the English Civil War, the Parliamentarians captured the isles, only to see their garrison mutiny and return the isles to the Royalists. By 1651 the Royalist governor, Sir John Grenville, was using the islands as a base for privateering raids on Commonwealth and Dutch shipping. The Dutch admiral Maarten Tromp sailed to the isles and on arriving on 30 May 1651 demanded compensation. In absence of compensation or a satisfactory reply, he declared war on England in June. It was during this period that the Three Hundred and Thirty Five Years' War started between the isles and the Netherlands.
In June 1651, Admiral Robert Blake recaptured the isles for the Parliamentarians. Blake's initial attack on Old Grimsby failed, but the next attacks succeeded in taking Tresco and Bryher. Blake placed a battery on Tresco to fire on St Mary's, but one of the guns exploded, killing its crew and injuring Blake. A second battery proved more successful. Subsequently, Grenville and Blake negotiated terms that permitted the Royalists to surrender honourably. The Parliamentary forces then set to fortifying the islands. They built Cromwell's Castle—a gun platform on the west side of Tresco—using materials scavenged from an earlier gun platform further up the hill. Although this poorly-sited earlier platform dated back to the 1550s, it is now referred to as King Charles's Castle.
During the night of 22 October 1707, the isles were the scene of the Scilly naval disaster, when out of a fleet of 21 Royal Navy ships commanded by Admiral Sir Cloudesley Shovell, six were driven onto the cliffs. Four of the ships capsized, with at least 1,450 dead, including the admiral, who was murdered by robbers on the beach. The probable cause was poor navigation. However, inability to accurately calculate their longitude is thought to have been a contributing factor.
The islands appear to have been raided frequently by Barbary pirates.
Governors of Scilly
An early governor of Scilly was Thomas Godolphin, whose son Francis received a lease on the Isles in 1568. They were styled Governors of Scilly and the Godolphins and their Osborne relatives held this position until 1834. In 1834 Augustus John Smith acquired the lease from the Duchy for £20,000. Smith created the title Lord Proprietor of the Isles of Scilly for himself, and many of his actions were unpopular. The lease remained in his family until it expired for most of the Isles in 1920 when ownership reverted to the Duchy of Cornwall. Today, the Dorrien-Smith estate still holds the lease for the island of Tresco.