Thietmar of Merseburg
The earliest surviving references to the city are found in the chronicles of Thietmar of Merseburg written between 1012 and 1018: ("bishop of Poznań", in an entry for 970) and "ab urbe Posnani" ("from the city of Poznań", for 1005). The city's name appears in documents in the Latin nominative case as "Posnania" in 1236 and "Poznania" in 1247. The phrase "in Poznan" appears in 1146 and 1244.