I was making the trek back from the Vatican-side of the Tiber to the historic center, when I noticed on my map that I was within blocks of Ara Pacis. Now you're probably saying to yourself "I know a lot of Rome and have never heard of Ara Pacis, or if I have, I hadn't given it a second though." Well, my friend, my advice to you is to put it on your "to do" list next time you're in Rome.
Ara Pacis is a beautifully restored altar of peace that was built around 13 BC to celebrate Augustus' victories abroad and the peace that followed them. The friezes along the walls show various people (in near-life size) from ancient Rome who are walking toward the west to celebrate the peace. The interior of the altar was used for the sacrifice of cows and other livestock in the name of this new-found peace.
The altar was originally closer to the Field of Mars, further south in the city. It was covered for hundreds of years by floodwaters and mud and was gradually rediscovered and identified by scientists familiar with Augustus' reign. Mussolini moved the altar to its current location, quite nearby the Mausoleum of Augustus, in an attempt to create a theme park of sorts in tribute to Augustus.
Today the altar is housed in an incongruously modern building that fills the interior with natural light and allows visitors on the inside to feel as if the altar is still outside.