According to the monk Bede, writing in his "Historia ecclesiastica gentis Anglorum" in the 8th century, the Anglo-Saxon age began when three tribal groups from Northern Germany and Southern Denmark – the Saxons, Angles and Jutes – began to migrate into Britain, where they were initially employed as mercenaries by the indigenous Romano-British population following the collapse of Roman Imperial rule. Archaeological evidence corroborates this, but also indicates the likely presence of a fourth continental tribal group settling in Britain during the 5th and 6th centuries, the Frisians. It is likely that the new settlers did not adhere strictly to their old tribal and ethnic ties, with new syncretic blends developing and new identities forged as they mixed with one another and with the indigenous British population. There is evidence that these colonists maintained ties with the Germanic-language cultures of Scandinavia, Germany and Northern France; they certainly traded with these societies for luxury goods, and told epic stories such as "Beowulf" which were set in their ancestral lands.