Old English initially was a diverse group of dialects, reflecting the varied origins of the Anglo-Saxon kingdoms of Britain. The Late West Saxon dialect eventually became dominant. Written Old English of 1000 AD was similar to other Germanic languages such as Old High German and Old Norse in terms of vocabulary and grammar. Written Old English is relatively unintelligible today, in contrast to written Modern English and written Middle English. Close contact with the Scandinavians resulted in much grammatical simplification and lexical enrichment of the English language, which had been based on Anglo-Frisian. These changes did not reach South West England until the Norman invasion in 1066. Old English developed into a full-fledged literary language, based on the most common manner of speaking in London during the 13th century.