The departure of the Romans was followed after a brief interval by the English Conquest, and London decayed--we may even say fell into utter desolation. For her greatness had been entirely commercial; she had had large trade with the Continent, which was now broken to pieces. She had received her food from ships which came both up and down the Thames, but the poor Britons who were fighting for existence had no more to send her. The rich traders and merchants had no longer any occupation, and left their luxurious homes to find it elsewhere. And so the once flourishing London became deserted.
But when the English Conquest was accomplished, and peace for a while followed warfare, a population also reappeared in London, consisting of traders who saw the great advantages of its situation. Prosperity began to return. London became once more a city of merchants. It was again flourishing when the heathen English were converted to Christianity by Augustine, so much so that in 604 one of his companions, Mellitus, became its first bishop, Sebert being then king. Sir Walter Besant sees in the identity of the Cockney dialect ("lydy" for lady, &c.) with that of Essex, a proof that the new population were chiefly from the East Saxons.
At first the Christianising of London seemed to be a failure. Mellitus built a cathedral, but had to flee before the heathenism into which the king's sons relapsed. The failure, however, was but temporary, and the Church became altogether triumphant. The intense sense of nationality, which has always characterised the English people, comes out in the names given to the London churches. The greater number of them were dedicated to English saints, and the names continue to this day. One of these saints--Botolph--who had endeared himself immensely to the Londoners, went forth to N.E. England and established a great mission there, and there he died. The noble tower of Boston (== Botolph's town) preserves his memory in Lincolnshire. But the Londoners, in love and veneration to his memory, built churches bearing his name at all the four gates which led towards his burial-place; three of them still remain, and the name of the fourth survives in Botolph's Lane, by Billingsgate.