Julius Caesar first landed in Britain on August 26th, 55 BC, but it was almost another hundred years before the Romans actually conquered Britain in AD 43.
Having subdued Gaul, or so it seemed at the time, Julius Caesar launched an expedition to Britain. It was late in the campaigning season and it is doubtful if he was bent on conquest, more likely a reconnaissance in strength. He would certainly have hoped to increase his prestige at home and he might have wanted to postpone a recall to Rome, where his enemies could get at him. He was probably encouraged by some British chiefs, hoping to use the Romans as allies against rival tribes. Whatever Caesar's intentions, he was defeated by the British weather.
A Gaulish chieftain named Commius was sent across the Channel to enlist support for the Romans among the British tribes, while a trusted officer took a fast galley to reconnoitre the coast. Caesar assembled eighty ships at Boulogne to carry two legions, the Seventh and the Tenth, plus irregulars, altogether some 12,000 men. The cavalry and their horses were to sail separately from Ambleteuse, a few miles north.
After waiting for a wind the Roman ships left Boulogne in the early hours of August 26th and came in sight of the white cliffs of Dover around 9am. The cliffs were bristling with menacing British warriors, horsemen and war chariots. It was obviously no place to land, but Caesar waited for hours offshore for the cavalry, which had got penned in Ambleteuse by tide and wind. In the afternoon the Roman fleet sailed north-east without them to pass the South Foreland and come in sight of the long stretch of flat shore to the north. The Britons moved along on land to keep pace.