Pantheon

The Pantheon is the best-preserved building of Ancient Rome and, nearly two thousand years after Emperor Hadrian completed it around AD 125, its concrete dome is still the largest unreinforced dome in the world. The bronze inscription on the porch credits Marcus Agrippa, whose earlier temple burned on this spot; Hadrian rebuilt it entirely but kept his predecessor's name, a gesture of imperial modesty that has confused visitors ever since.

Step through the massive original bronze doors and the architecture does something no photograph captures: a perfect sphere would fit exactly inside the rotunda, the dome's diameter equal to its height. The only light source is the nine-metre oculus at the crown, open to the sky, which sweeps a moving disc of sunlight around the coffered ceiling through the day. When it rains, the water falls through and drains away through discreet holes in the sloping marble floor.

The building survived because it was consecrated as the church of Santa Maria ad Martyres in AD 609, and it remains a working church today. Inside are the tombs of the painter Raphael and of Italy's first two kings, Vittorio Emanuele II and Umberto I. Piazza della Rotonda in front, with its obelisk-topped fountain, is one of the liveliest squares in the historic centre.

The Pantheon sits in the pedestrian heart of Rome, an easy walk from Piazza Navona, the Trevi Fountain and Campo de' Fiori; there is no metro stop nearby, so arrive on foot or by bus to Largo di Torre Argentina. Come at opening for the emptiest rotunda, or near a sunny midday to watch the oculus beam at its most dramatic.

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