Ancient Britain was a peninsula until a tsunami flooded its land-links to Europe some 8,000 years ago. Did that wave help shape the national character?
The coastline and landscape of what would become modern Britain began to emerge at the end of the last Ice Age around 10,000 years ago.
What had been a cold, dry tundra on the north-western edge of Europe grew warmer and wetter as the ice caps melted. The Irish Sea, North Sea and the Channel were all dry land, albeit land slowly being submerged as sea levels rose.
But it wasn't until 6,100BC that Britain broke free of mainland Europe for good, during the Mesolithic period - the Middle Stone Age.
It is thought that landslides in Norway - the Storegga Slides - triggered one of the biggest tsunamis ever recorded on Earth when a landlocked sea in the Norwegian trench burst its banks.
The water struck the north-east of Britain with such force it travelled 25 miles (40km) inland, turning low-lying plains into what is now the North Sea, and marshlands to the south into the Channel. Britain became an island nation.
At the time it was home to a fragile and scattered population of about 5,000 hunter-gatherers, descended from the early humans who had followed migrating herds of mammoth and reindeer onto the jagged peninsula.
"The waves would have been maybe as much as 10m (33ft) high," says geologist David Smith, of Oxford University. "Anyone standing out on the mud flats at that time would have been dismembered. The speed [of the water] was just so great."
At Montrose, on the north-east coast of Scotland, Smith has uncovered signs of this long-ago natural disaster. A layer of ancient sand runs through what should be banks of continuous clay - sand washed inland by the inundation.
Relics of these pre-island times are being recovered from under the sea off the Isle of Wight, dating from when the Solent was dry land.
Grooved timbers preserved by the saltwater are thought to be the remains of 8,000-year-old log boats, and point to the site once being a sizable boat-building yard, says Garry Momber, of the Hampshire and Wight Trust for Maritime Archaeology (see video clip below).
The tsunami was a watershed in our history, says archaeologist Neil Oliver, presenter of BBC Two's A History of Ancient Britain.
"The people living in the land that would become Britain had become different. They'd been made different. And at the same time, they'd been made a wee bit special as well."
Being so closely bordered by water meant boat-building and seafaring became a way of life. Many millennia on from the tsunami, the British sailed the ocean waves to find new lands and build an empire.
Its more recent history bristles with naval heroes, sea battles and famous explorers. English, Scottish, Welsh and Irish migrants left their homelands to settle far and wide. And Elizabeth I was not only a notable monarch for being a woman, but for presiding over a famous naval victory, and English forays into New World exploration.
But the idea of England - in particular - being a maritime nation has its roots as much in spin as in reality, says Dr Nigel Rigby, of the National Maritime Museum. An early exponent was the 16th Century writer Richard Hakluyt, who promoted the settlement of North America.
Hakluyt's writings played on the growing desire to seek new territories after the loss of Calais in 1558.
"Hakluyt's Voyages spun the idea that the English had always been stirrers and searchers abroad. But it was not really an island that had started to see a future at sea."
By the time Charles I took the throne, the lure of maritime power had taken hold. "He called his great warship the Sovereign of the Seas. It was a statement of intent," says Rigby.
For hundreds of years, ships, goods and people moved to and from the British Isles. Merchant and naval ships alike were staffed by those from far and wide, some of whom settled in its ports.
But just as Britain could reach out to the world from its safe harbours, so, too, could the world reach in - and this fuelled feelings of vulnerability, says Rigby. If an invader can make it across one's watery defences, the British coastline offers an abundance of places in which to make landfall.
"The 19th Century writer Alfred Thayer Mahan made the point that if you look at the coastline of Britain, it's suited to maritime trade with good harbours. But easy access for trade means it's also vulnerable to attack from the sea.
"In times of national threat, this is a recurring fear. Hence the importance of being able to defeat enemies at sea," says Rigby.
Mahan's writings underlined the sense of Britain as an island nation, defined by its relationship with the sea. This identity was further bolstered by the likes of the novelist Erskine Childers, who wrote The Riddle of the Sands, a spy novel in the early 20th Century about a German plot to invade from across the North Sea.
"The idea of an 'island nation' is something of a cultural construct," says Rigby.
"But in Britain you are never more than 60 miles from the sea. So it's important to be able to defend the coastline, and to be able to make a living from all around that coastline too."
Many believe its island status has also shaped Britain's rather detached attitude to Europe today, which is still often referred to as "the continent".
In the past, historian David Starkey has argued that Henry VIII's break from the Catholic Church in Rome made him the first Eurosceptic.
"In plans for the elaborate coastal defences that Henry commissioned we can see how England no longer defined itself as part of Europe, but as separate from it - a nation apart," he wrote in the Camden New Journal.
"Catholic Europe was now the threat, the launch pad for invasion. In other words Henry was the first Eurosceptic: the xenophobic, insular politics he created have helped to define English history for the past five centuries."
Find out about ancient sites, and activities relating to ancient Britain, on the BBC Hands On History website.