I'm finding this debate quite interesting as many of the Medieval towns
and cities in England and Wales are actually built on a grid system.
This has been caused by the fact that most of the early towns in England
are built on flat land and are Roman in origin. The Romans laid there
cities out in Grid fashion with only major highways cutting the cities
at perculiar angles.

The majority of the original English and Welsh towns that were
present at the time of the Norman invasion (1066 AD) such as York,
London, Winchester, Chester, Cardiff, Cirencester and colchester are
Roman in origin. Also many of the initial Norman castles of any
strength, were actually built buy the Romans (Saxon Shore Forts).

The Grid system can be seen in many "Roman" european cities, the
best example I've seen is Verona which is still layed out in this way.

People have talked about city sizes and the presence of walls
around these cities. Most of those cities I have named still possess
remnants of their Roman walls to this day. The best example of this is
York which still has its walls altough greatly repaired by the
Victorians. These are approximately 4 and a half miles in circumference
giving the "Inner" city an area of about 2 square miles. This was home
to about 50,000 to 100,000 souls through most of the Medieval period
although it fluctuates with plague and Scottish invasions.

> >The city I live in was founded almost 250 years ago, and for the
> >most part you can't find a straight street in it. Wy you ask?
>
> One thing that many Americans may not realise is that most cities will
> look a complete mess from overhead. Cities tend to evolve from towns
> which in turn evolve from villages, which will be strategically placed
> at river crossings, river junctions, or hills. This does not make for
> 'nice' layouts, which can be quite annoying for the poor sap trying to
> make up a realistic looking city map.
>