This chapter focuses on street alignment and especially sidewalks – a key device in town planning but one that was experienced at the micro-scale by city dwellers. Invented during antiquity in the Mediterranean world, the sidewalk system disappeared during the Middle Ages before reappearing in the 17th century along docks and bridges and then along the streets. Since the first sidewalks in Brussels, their construction was the responsibility of the riparian owners, but Alderman Auguste Blaes proposed a compromise, with a decreasing bonus system to accelerate construction. Stricto sensu alignment is defined by Bernard Gauthiez as the line on which buildings are placed. From the 13th century, it was one of the first tools used by urban authorities to manage the public space. The alignment defined the boundary between private property and public space: an owner who wanted to rebuild his plot had to ask the authorities the alignment on which to draw his facade.