The Pantheon is old. Really, really old. Originally a temple to the seven deities of ancient Rome, it was built in about 27 BC by Marcus Agrippa (who, not a modest man, had this achievement etched in large letters across the front of the building, above the portico). Agrippa’s temple survived only till about 80 AD, when it was completely destroyed by fire. In 125 AD, however, the Emperor Hadrian got the monument rebuilt- even going so far in his magnanimity as to get Marcus Agrippa’s pompous inscription etched on it.

Although it’s suffered the ravages of time (and man- marble and bronze were torn off the building to be used elsewhere), Hadrian’s structure is the Pantheon one sees today. In the early years of the 7th century, the Pantheon was gifted by the Byzantine emperor Phocas to the Pope, who consecrated it and made it the church of St Mary and all the Martyr Saints.

We arrived at the Pantheon shortly before sunset and found it brimming with tourists. We spent some time admiring the awesome granite columns of the portico, the obelisk that stands in the piazza outside, and the flattish concrete dome (it was once covered with bronze plates) of the building. By the time we finished, much of the crowd had gone, so in we went, through massive bronze doors that were originally goldplated.

Outside, the Pantheon looks like a typical Roman temple; inside, the ancient Roman style is tinged with touches of the Renaissance. We sat for a while on the chairs that line the walls, and looked around. The circular interior is largely a blend of dark marble, predominantly red, green and brown. Niches along the walls hold Biblical statues, many of them carved by famous Italian sculptors. The tomb of Raphael, for instance, is surmounted by a Madonna carved by one of Raphael’s students.

But most arresting of all is the oculus- the `Great Eye’ of the Pantheon. The oculus is a large circular opening that pierces the centre of the dome, and lets in sunlight (and rain!). We watched the last rays of the setting sun streaming in through the oculus, forming an elongated sphere of light on the floor. We admired the statuary in the niches, marvelled at the sombre beauty of the place, and then, when it got too dark, reluctantly took ourselves off.

Entry to the Pantheon is free. Try to time your visit for when the sun’s high in the sky, so you get the full effect of the oculus. And since this is a church, keep your shoulders and knees covered.

The entrance is through huge bronze doors, and the interior is a circular room with Catholic alters and artifacts. The dome has a span of 43.2 m (142 feet).

One of the fascinating architectural aspects of it is the "oculus", a circular hole in the ceiling which allows in rain and sunlight.

It is open from 8:30am to 7:30pm. Admission is free.

Right outside the Pantheon is the Piazza della Rotonda, a lively square filled with cafes, bars, and restaurants. It is especially lively in the summer, when the Pantheon is lit from below and stands as an enormous reminder of the grandeur of ancient Rome.

Even though this is one of the best-preserved pieces of Roman architecture, don't forget it's still a functioning Catholic church, with regular services, so be aware that it's not always open for tourists. It's often crowded on the weekends, so I'd recommend visiting during the week.