The founding date of Utrecht is around 50 CE and as usually related to the construction of a Roman fortification (Castellum). In Roman times the name of the Utrecht fortress was simply Trajectum. Trajectum became in Dutch 'Trecht'. The U comes from Old Dutch 'uut' meaning downriver. The location on the banks of the river Rhine allowed Utrecht to become an important trade centre in the Northern Netherlands. The town Utrecht was granted city rights by Henry V in 1122. At this moment Utrecht is the fourth largest city of the Netherlands with a population of 310.000.