Like all of Rome, the Colosseum is layered with signs of contruction, destruction, rebuilding, and reuse. These underground chambers were originally constructed in 80 AD, but have clearly been repaired many times since. Artifacts from the past have been treated with varying levels of respect: here a piece of marble with an inscribed "L" (the white piece in the center of the photo) was used to repair the masonry.

We were somewhat surprised to see how much of the Colosseum is actually brick. Here a bit of crumbled wall gives a view to its more familiar gray travertine outer walls, and the pock marks on the inner wall are holes for bronze anchors which supported a marble facade.

Notions about how to preserve the past change over time. In the 1500's the Colosseum was crumbling, and civil engineers, concerned about the safety of people using it, stabilized the ruins by simply filling the unstable areas with concrete. This undoubtably saved the Colosseum from collapse, and maybe someday we will be able to remove the concrete and find that the structures underneath are far better preserved than their exposed counterparts, which contine to be slowly eroded by plants, pollution, and tourists. A few rows of marble seats have been excavated. These were reserved for the elite, who likely brought cushions to sit on during the performances.

An earthquake in 443 caused major damage, possibly resulting in the construction of the much-newer-looking area to the right of this photo. The arena was used for games and hunts into the 6th century.

The basic three-layer structure of the Colosseum was still intact at that time. In the 6th century, the inner arena was repurposed as a graveyard, and the vaulted areas rented out for housing and shops through the 12th century. In the 13th century it was fortified and used as a castle. In 1349, an earthquake destroyed the outer wall of the south side. The ruined building became a rock quarry, used for building materials all over Rome. The intact northern section became the quarters of a religious order.

Salvation for the Colosseum came from an unlikely source: the Catholic church. Pope Benedict XIV declared the site sacred, claiming that it was the place of death of martyrs. In fact there is no record of martyrdom at the Colosseum, although undoubtably some early Christians met their deaths there, along with other prisoners of the Romans. Evidence suggests that the martyrs were to save the structure, not the other way around. Quarrying at the Colosseum stopped with this dedication.

Modern excavation at the site has resulted in a number of column parts placed here and there around the Colosseum.

One interesting question is what to save. In addition to the archaeological finds, there are 200 species of vegetation living among the rocks of the ancient building. In 1855 420 species were counted, but just a few years later concerns that the vegetation was destroying the structure led to a vast project to remove all vegetation from the Colosseum. It has been proposed that the many exotic animals brought to the Colosseum brought exotic plant seeds with them.