Carfax is the centre of town, the ground slopes down from all points, an important thing for mediaeval towns that depended on gravity and the rain to wash all their detritus to where the river would swill it all away. In the north it got washed into the moat, fish ponds or town ditch of what was to become Broad St. In the south it got washed down to the Thames swamp which began at the lower end of Christchurch. When William the Conqueror took over England, he was appalled at the crudity of our economics, only just emerging from an era of barter. So as to revolutionise this system he imported Jews from his home of Rouen who understood the mechanics of Credit. Under Royal privilege, he installed Jews in the major towns, including Oxford where they settled on either side of St Aldates in what is now the Town hall and Christchurch and along the other side of the road as well where the Post Office is.