Photo: Morgan Galpin, CC BY-SA 4.0 via Wikimedia Commons
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Ara Pacis is an altar to peace commissioned by the Roman Senate on 4 July 13 BC to honor the triumphal return from Hispania and Gaul of Augustus. It is universally recognised as a masterpiece. Following discovery of this work under a building in Rome, Mussolini built a protective building for it near the Mausoleum of Augustus, where it was reconstructed. A new building on the same site as Mussolini's was opened in 2006 and has been controversial. The mayor at the time said he would tear down the new structure. The basement of the new building features occasional exhibitions. You can see much of it from outside the building. Paying to go inside adds some background info, but not much more.
Mausoleum of Augustus
This is a large tomb built by the Roman Emperor Augustus in 28 BC in the form of a stone ring covered by an earth mound. A brick wall, 87 m in diameter, carried an earth mound covered with cypresses. On top of the hill stood a bronze monument of the emperor. The building was 44 meters high. At the beginning of the alley, which led to the tomb were two Egyptian obelisks. On both sides of the doorway bronze plates describe the "Res gestae", the deeds of the emperor. The urns of Augustus, Marcellus, Octavia, Agrippa, Drusus and other members of the Julian Claudian dynasty were revered here. In the Middles Ages the building served as citadel of the Colonna family. It was destroyed by Pope Gregor IX in 1241. The body of Cola di Rienzo. a popular leader of the people in the mid-14th century, was burnt in this monument. The Mausoleo di Augusto is not open to the public, and is fenced off.
Catacomb of Priscilla
Underground burial place of an ancient Roman family and of seven early popes.
This is a treasure-trove of art. There are a couple of paintings by Caravaggio: "The Crucifixion of Saint Peter" and "The Conversion of Saint Paul" (in a dim alcove to the left of the altar, both at right angles to the viewer, with a machine wanting €2 to switch on the lighting) together with a sculpture by Bernini, frescoes by Pinturicchio and mosaics by Raphael. Part of the Dan Brown tour, this church featured in Angels and Demons, although the Vatican did not allow filming inside.
Baroque church more noted for its position at the top of the Spanish Steps than it is for the church. Backdrop for numerous movies including Audrey Hepburn and Gregory Peck in Roman Holiday.
Rome's Mosque
The Rome Mosque, which was inaugurated in 1995, is the biggest in Europe. The inside of the 30,000 m² structure has a large prayer hall that uses tri-stemmed columns that imitate the features of trees.