A faceted brick wall stands in the middle of Venice’s Arsenale, like a sharply creased origami screen, blocking the route of visitors to this year’s Architecture Biennale. As you get closer, it looks like a rubble tapestry, with pieces of crushed brick and coloured glass emerging from its gnarled surface like great chunks of mineral nougat. Fine geometric patterns are etched across its facets, adding an air of handmade embroidery. On a wall nearby hang images that explain the origins of this arresting barrier: a reproduction of a 17th-century map of the coasts of Africa and Brazil, a slave-trading ship’s...