The Plane of Piazza San Cosimato

The neighbourhood had this tree scanned. Volunteers in Trastevere paid forest agronomists to run a tomography on the trunk, reading the internal soundness of the wood the way a hospital reads a body, because the tree stands directly over the square's children's play area and nobody wanted to guess. At 5.65 metres around it holds the thickest plane trunk on Rome's monumental register, thicker than the celebrated planes of Villa Borghese, and it grows not in a cardinal's garden but in a working piazza with a morning market, a football pitch's worth of parked scooters and a tenth-century church. The square was open pasture until the 1880s, the Prati di San Cosimato, grazing land outside the tight medieval lanes. When Rome became the capital and Trastevere was rebuilt, the fields became a triangular market square, and the plane either survived that or was planted into it; no document says which, and its 2013 addition to the register recorded size without age. Platanus x acerifolia is itself an accident, an eighteenth-century hybrid of the eastern and American planes that turned out to tolerate city air better than either parent. Rome planted thousands. This is the one the neighbours look after.