Research - The period setting for the model - 1250 A.D., the
middle of the 13th century - was chosen for a number of reasons.
Any reconstruction of the city in more remote periods (like that
of the Saxon burh or borough, c.900 A.D.) would have to be largely
speculative. For more recent periods the amount of detailed information
becomes so large that a major research project would be needed
to assemble it. But in 1250 the city wall had not long been built,
and all the city streets known in later centuries were established:
the familiar geography of the modern city centre was just emerging.