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Photo: Peter Gerstbach, CC BY-SA 3.0 via Wikimedia Commons
Built in 81 AD by the emperor Domitianus in dedication to his brother Titus, who died earlier that year and reigned as emperor from 79-81, overseeing the opening of the Colosseum in 80 and the eruption of Mt Vesuvius the previous year.
The Arch of Titus is a 1st-century AD honorific arch, located on the Via Sacra, Rome, just to the south-east of the Roman Forum. It was constructed in c. 81 AD by Emperor Domitian shortly after the death of his older brother Titus to commemorate Titus's official deification or consecratio and the victory of Titus together with their father, Vespasian, over the Jewish rebellion in Judaea.
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Arco di Costantino
Located a short walk west of the Colosseum, this well-preserved monumental arch was erected (soon after 315) to commemorate the victory of Constantine, the first Christian emperor, over his rival Maxentius at the Battle of the Milvian Bridge in 312. In general design, the Arch of Constantine imitates the century-earlier Arch of Septimius Severus (nearby in the Forum). The three arches are decorated utilizing mainly materials plundered from other imperial monuments by Trajan, Hadrian and Marcus Aurelius. The quality of its sculptural decoration, however, betrays the slow degradation that Classical Roman sculpture had experienced in the 3rd century AD.
Tempio di Antonino e Faustina
Built in 141 AD and dedicated to the Empress Faustina; after her husband emperor Antoninus Pius died in 161 AD the temple was rededicated to the couple.
Known properly as the Flavian Amphitheatre, this most famous of Roman landmarks takes its name from the giant statue of the emperor Nero that once stood near this location. The amphitheatre was capable of seating 50,000 spectators for animal fights and gladiatorial combats. It was a project started by the Emperor Vespasian in 72 and completed by his son Domitian sometime in the 80s. The Colosseum when completed measured 48 m high, 188 m in length, and 156 m in width. The wooden arena floor was 86 m by 54 m, and covered by sand.;
Expect a long queue and an even longer wait. You can skip the queue if you decide to take a tour, but if you don't want a tour, you can STILL skip the queue. If you walk to the entrance for the Roman Forum, you can buy tickets there which allow you to bypass the queues. You can also buy tickets online. There are lots of people offering tours in English just outside the entrance to the Colosseum. Inside you can take a tour (English, Spanish, or German) every 30 minutes or so for an additional fee. The tours are given by knowledgeable archeologists, but they don't take you to any areas you couldn't visit on your own.
Tempio di Divo Giulio Cesare
Finished in 29 BC, marks the spot of Caesar's spontaneous cremation and Mark Antony's funeral speech, made famous by Shakespeare in his play Julius Caesar ("Friends, Romans, Countrymen, lend me your ears ...").
Completed in 179 BC.
Contains the ruins of several large villas that belonged to wealthy Roman families. You can buy a combined ticket for the Palatine Hill, the Roman Forum and the Colosseum here, avoiding the long lines at the Colosseum. While the Imperial and Roman Fora are probably more spectacular, overall, there are amazing sights on the Palatine Hill, so unless you are terribly short on time or find it too challenging to climb the hill, allow an hour or more for these sights, too.