I went to Brussels to photograph a World Heritage site and came home with a picture of the sky. The Grand-Place is in the frame, barely. A sliver of the Town Hall on the left with its rank of statues on corbels, a run of gabled houses on the right, and between them a long grey wedge with two aircraft trails crossing it.

Everything below the rooflines is legally frozen. The square went onto the UNESCO list in 1998, and the protection is granular in the way heritage protection always is. Shopfront lettering, paint, the mortar you point the brick with, the colour of an awning. There is a whole apparatus of committees deciding what a facade is allowed to look like, and it applies to a strip of city about two hundred metres long.