A sanctuary to Mithras in Ostia Antica. The impressive sculptural tauroctony is a plaster cast of the original, now housed in Ostia's museum. Like many mithraea, this one resembles a natural cave. Even when Ostia swelters in the summer heat, the mithraeum remains cool, damp, and secret.

One of the best preserved mithraeums in Ostia Antica. The detailed astronomical mosaics along the platforms and the black arcs across the aisle's floor are too faded to see easily in this photo, but provided important clues to discovering the cult's beliefs.

The mosaic representation of Cautes, the upright torchbearer, at the beginning of the aisle in the Mithraeum of the Seven Spheres, Ostia Antica.

The mosaic aisle of this mithraeum in Ostia Antica still preserves the symbols of each progressive Mithraic rank, from Corvus to Pater.

Open only by once-monthly guided tours, this mithraeum is located beneath the modern Church of Santa Prisca in Rome. It's famous not only for its large, hatless sculpture of Mithras, but also for its remaining frescoes, which show the procession of ranked initiates.

This headless Cautes statue stands in a niche at the beginning of the aisle in the Mithraeum of Santa Prisca. An empty niche for Cautopates stands opposite it.

This mithraeum lies beneath the Basilica of San Clemente in Rome. A remarkable site, the above-ground church was built in the 1100s atop the remains of an earlier church from the fourth century AD. Beneath that earlier church lies the mithraeum, complete with the altar and sanctuary pictured here and another chamber that may have contained a Mithraic "schoolroom."

The best preserved Roman temple in the world. Now a Roman Catholic church, its exterior remains a masterpiece of ancient architecture.

The ceiling of the Pantheon, with its oculus open to the sky. The dome is made of concrete and remains an architectural marvel. Despite the perennial crowds, I find the Pantheon a deeply spiritual place the moment you turn your face upward.

Despite the Christian statuary and paintings, its easy to imagine the Pantheon in its original form, as a temple to the Olympians. The marble is all original.

The Roman arena, lit at night, serves as an unmistakable reminder of the Empire's glory days.

Now the doors to the Basilica of St. John Lateran, the oldest basilica in Rome, these are the original bronze doors from the Curia, or Roman Senate House.

The Temple of Saturn in the Roman Forum. Once, the Romans stored their Imperial treasury beneath it.

Roman Forum. The chief priest (usually the emperor) appointed six women at a time to serve as Vestals, dedicated to the goddess Vesta (Hestia). Each served for 30 years. If, in that time, she lost her virginity, she was executed by being buried alive.