To the Romans of the 1st Century BC, Britain was a semi-mythical land beyond the seas, populated by barbarous, war-like tribespeople known as the Pretani or Britons.
Thanks to Caesar's book, the invasions have been described as the first recorded events in the entire history of the British Isles.
But until the Roman landing place in 54 BC was identified near a beach in the southeast of England, there was no archaeological evidence for Caesar's invasions.
A defensive ditch from the fort was first discovered in 2010, by archaeologists who excavated the area as part of local government requirements before a new road was built there.
The remains of Roman weapons found at the site and clues about the local landscape in Caesar's Commentaries show the fort was built by the Romans to keep watch over the hundreds of ships of their invasion fleet at anchor in Pegwell Bay, the researchers say.
Romans in the UK
In the first, which historians date to 55 BC, Caesar invaded with two legions of infantry and fought the British for 10 weeks in the eastern parts of Kent, before retiring his troops to Gaul for the winter.
IN 54 BC, Caesar invaded again, with time with 5 legions of Roman infantry and 2000 cavalrymen – more than 20,000 men in total – near the Roman fort discovered by archaeologists at Ebbsfleet.
In the months that followed, the Roman armies waged war through Kent and across the River Thames into the modern counties of Essex and Hertfordshire, where Caesar forced the surrender of the British war leader, Cassivellaunus.
After imposing peace treaties on the defeated southeast British tribes, Caesar returned with his troops in September 54 BC to Gaul, where a poor harvest had caused unrest.
Changes in the coastline
Caesar described leading a fleet of more than 800 ships carrying more than 20,000 Roman soldiers for his second invasion of Britain in 54 BC.
He claimed there were so many ships that the British warriors gathered to oppose the Roman invasion took fright, and fled to hide in an area of higher ground near the landing site – probably the cliffs near Ramsgate that can be seen on the upper left of this image, say the researchers.
Positioned for security
The channel was filled in by land reclamation and a natural process of silting up in the Middle Ages.
The archaeological team from the University of Leicester studied LIDAR surveys of the terrain of the Isle of Thanet to learn how the shore of the Wantsum Channel would have looked in the 1st Century BC.
They discovered the fort at Ebbsfleet was situated on a peninsula of land jutting out from the south side of the island, placed where a garrison could keep watch of the ships of the Roman invasion fleet at anchor in the tidal waters of Pegwell Bay.
They found that the defensive ditch around the fort was built in the same way as Roman military forts known to have been built by Caesar's troops in France and Germany within a few years of 54 BC.
They also found the remains of people who appeared to have been killed in conflict, local pottery fragments that date the ditch to the 1st Century BC, and pieces of iron weapons.
The find matches pila found in the parts of southern Gaul where Caesar recruited the troops for his legions, and in Germany where they fought.
Ships of war
This model of a Roman galley shows the type of warship used in the invasion fleet. It is based on a graffito found at Alba Fucens in Italy.
Lost in the dark
But according to Caesar, whose words are shown in this map, the Roman fleet lost its way in the darkness when the wind fell and the tide in the English Channel carried them too far north.
At sunrise, Caesar says, the Roman spotted land "afar left" – behind them, and to port. The archaeologists think this land described by Caesar was the high cliff around Ramsgate at the northern end of Pegwell Bay.
Changes to come
The peace treaties imposed on the tribes of southeast of Britain established the tribal rulers as "client kings" who earned power and prestige from their alliances with Rome, the researchers say.