How Was Roma Built

Rome was built, demolished and rebuilt out of itself, and the method is visible everywhere.

Roman concrete

The Romans mixed lime with pozzolana, the volcanic ash from the Alban Hills, producing a concrete that sets underwater, gains strength over centuries and appears to repair its own cracks through lime clasts reacting with water. It is why the Pantheon’s 43-metre dome has stood unreinforced since AD 126, with the aggregate graded from heavy basalt at the base to light pumice at the crown and a hole left open at the top to remove the weight.

Facing

The concrete core was faced in brick or small stone and then, on important buildings, clad in marble and travertine. The Colosseum’s pockmarks are the holes left where the iron clamps holding that facing were prised out for scrap in the Middle Ages.

Spoliation

For a thousand years, ancient Rome was the quarry for medieval and papal Rome. Columns were carried into churches, marble was burned for lime, and Saint Peter’s took travertine from the Colosseum. Very little was destroyed maliciously; it was simply used.

Reuse

The Pantheon survived because it became a church in 609. Piazza Navona keeps the shape of Domitian’s stadium because houses were built on the seating. Castel Sant’Angelo is Hadrian’s tomb with a fortress on top.

Obelisks

Thirteen ancient Egyptian obelisks stand in Rome, more than in Egypt — brought as imperial trophies, buried and forgotten, then dug up and re-erected by Renaissance and baroque popes as waymarks at the end of long straight streets. Moving and raising them was a major engineering feat each time, and they still function exactly as intended, pulling the eye across the city.

The nineteenth century

Unification brought ministries, the embankments and the vast Victor Emmanuel monument that Romans have never forgiven.