From Sant’Ignazio, Via del Seminario leads down to Piazza della Rotonda, where the main focus of interest is the Pantheon, easily the most complete ancient Roman structure in the city and, along with the Colosseum, visually the most impressive. Though originally a temple that formed part of Marcus Agrippa’s redesign of the Campus Martius in around 27 BC – hence the inscription – it’s since been proved that the building was entirely rebuilt by the Emperor Hadrian and finished around the year 125 AD. It’s a formidable architectural achievement even now: the diameter is precisely equal to its height (43m), the hole in the centre of the dome – from which shafts of sunlight descend to illuminate the musty interior – a full 9m across. Most impressively, there are no visible arches or vaults to hold the whole thing up; instead they’re sunk into the concrete of the walls of the building. It would have been richly decorated, the coffered ceiling heavily stuccoed and the niches filled with the statues of gods, but now, apart from its sheer size, the main things of interest are the tombs of two Italian kings, and the tomb of Raphael, between the second and third chapel on the left, with an inscription by the humanist bishop Pietro Bembo: “Living, great Nature feared he might outvie Her works, and dying, fears herself may die.” The same kind of sentiments might well have been reserved for the Pantheon itself.