Old English contained a certain number of loanwords from Latin, which was the scholarly and diplomatic lingua franca of Western Europe. It is sometimes possible to give approximate dates for the borrowing of individual Latin words based on which patterns of sound change they have undergone. Some Latin words had already been borrowed into the Germanic languages before the ancestral Angles and Saxons left continental Europe for Britain. More entered the language when the Anglo-Saxons were converted to Christianity and Latin-speaking priests became influential. It was also through Irish Christian missionaries that the Latin alphabet was introduced and adapted for the writing of Old English, replacing the earlier runic system. Nonetheless, the largest transfer of Latin-based (mainly Old French) words into English occurred after the Norman Conquest of 1066, and thus in the Middle English rather than the Old English period.