Why Old Streets Stay Where They Are

Walk through the oldest quarter of almost any European city and the street plan will be narrow, irregular and inconvenient. [A] It is also, in most cases, the plan that was there in the Middle Ages. [B] Buildings within it have been replaced many times over, some of them more than once in a century, and the lines between them have hardly moved. [C] The explanation is not affection for the past. [D]

A street is a boundary between holdings, and boundaries are recorded, taxed and inherited. Rebuilding a house requires one owner to act. Moving the street in front of it requires agreement from everyone whose land the new line would cross, and compensation for those who lose. The cost of the second operation does not fall as building technology improves, because it is not a building cost at all.

This is why the clearest exceptions are not periods of prosperity but moments when ownership was suspended. After a fire destroyed a district, or where a ruler held the land outright, plans were redrawn in a season. Elsewhere the medieval lines survived the arrival of the railway, the car and the office block, not because they suited any of them, but because each of those arrived as a private decision about a single plot, and a street cannot be moved one plot at a time.