The reason for London

The reason why London exists, why it is here and not there, and what it is, rarely comes to the mind of the millions of  Londoners, still less into the mind of policy chiefs, planners and politicians. Essentially, it is historical. London grew from the lowest point downstream that Romans could build a bridge  across the Thames - a difficult task since it involved not just the bridge over the river but also a causeway and smaller bridges crossing islands in a periodically flooded floodplain along the line of the Borough, in Southwark. It also coincides with the then highest point upstream that Roman boats could use the tide to bring goods upstream. The line of the North - South crossing can still be seen, as the Roman Road from the north followed a shallow ridge to the river, it has now sprouted enormous buildings. The deep historical structure is still a pervading influence
Click for a map of Roman London imposed on modern street map Picture below is of the road entering the City from Bishopsgate

The line of the Roman  road to Lincoln and York - Ermine Street - as it enters the walled city (marked by tall buildings today) and heads towards the river crossing to Southwark (Shard, under construction, now finished)

Map showing direction of photograph photo by Howard Kingsnorth (website)   http://www.guardian.co.uk/world/picture/2011/jan/28/london#zoomed-picture http://www.howardkingsnorth.com/urban.html