Around the mid-fifth century three Saxon keels cut through the waves towards the southern coast of Britain. They were not the first Germanic warriors or migrants to arrive since direct Roman authority had ended in the early fifth century and would not be the last. Yet the arrival of these particular warriors would prove to be a turning point in the history of these islands. The literary sources that survive point to the arrival of these mercenaries and their subsequent revolt as the pivotal event rather any invasion or mass migration. There have been many books on the Anglo-Saxons. Those that touch on the first arrivals deal only briefly with the fifth and sixth centuries due to the lack of historical records. This book is unique in focusing on the events mentioned by the sources such as Gildas and Bede. It will show that the former Roman Diocese limped on outside direct Roman rule for a generation, beset by constant raiding from Picts and Scots in the north and Saxons and other Germanic pirates in the south. It will look at Roman practices of hiring and settling mercenaries and Germanic groups across the empire. A comparison with these will provide important clues, as well as understanding how and why the diocese and provincial structure fell apart, allowing petty kingdoms to emerge in the sixth century. The subsequent centuries have been termed the Anglo-Saxon period. This book goes back to the very beginning, the adventus Saxonum: The Coming of the Saxons.