Original: Until recently the history of the Viking Age was largely based on Icelandic Sagas, the history of the Danes written by Saxo Grammaticus, the Russian Primary Chronicle and the The War of the Irish with the Foreigners.
Simplified: Until recently, what was known about the history of the Viking Age was based on the Icelandic Sagas, the history of the Danes written by Saxo Grammaticus, the Russian Primary Chronicle and the War of the Irish with the Foreigners.