10 most difficult Rome riddles

The Roman Theatre of Orange, France was built in the early 1st century. It is one of the best preserved of all Roman theatres and is currently used as a festival site called Chorégies d'Orange. In 1981, UNESCO declared the theatre as a World Heritage Site.

The Year of the Four Emperors, 69 AD, was a year in which four emperors ruled in succession. Between June of 68 and December of 69 Galba, Otho, and Vitellius successively rose and fell before the July 69 accession of Vespasian, who founded the Flavian dynasty.

The Quirinal Hill is one of the Seven Hills of Rome, at the north-east of the city center. It is the location of the official residence of the Italian head of state, who resides in the Quirinal Palace; by metonymy "the Quirinal" has come to stand for the Italian president. The Quirinal Palace has an extension of 1.2 million square feet.

The temple - 43 meter in diameter - was built by emperor Hadrian. Its dome with 8-meter wide oculus was built of unreinforced concrete that has been a mystery for ages. The weight of Roman concrete used to build the monolitic structure is merely 1/5 of common concrete. Such effect was achieved by mixing in of volcanic tuff and pumice.

Castel Sant'Angelo (English: Castle of the Holy Angel) was initially commissioned by the Roman Emperor Hadrian as a mausoleum for himself and his family. The building was later used by the popes as a fortress and castle, and is now a museum. The structure was once the tallest building in Rome.

Completed in AD 113, the Trajan's Column commemorates Roman Emperor Trajan's victory in the Dacian Wars. Originally, a 4.8 m bronze statue of Trajan stood on the top pedestal, but this was replaced by a statue of St. Peter in 1587.

The Colosseum was built by the three emperors known as the Flavian dynasty (Vespasian, Titus, Domitian). During the Ancient times, it was known in Latin as Amphitheatrum Flavium. The name "Colosseum" had been coined to refer to the amphitheatre around year 1000 AD.

Roman nomenclature is somewhat different from the modern English form. Gaius, Iulius, and Caesar are Caesar's praenomen, nomen, and cognomen, respectively. In modern usage, his full name might be something like "Gaius Iulius, the Caesar", where 'Caesar' denoted him as a member of the 'Caesarian' family branch of the 'Iulian' clan, and 'Gaius' was his personal name.

The Altar of the Fatherland is a monument built in honor of Victor Emmanuel, the first king of a unified Italy. The structure is 135 m wide and 70 m high, making it the largest monument in Rome. Its base houses the museum of Italian Unification. In 2007, a panoramic lift was added to the structure, allowing visitors to ride up to the roof for 360-degree views of Rome.

The Umbilicus Urbis Romae ( "Navel of the City of Rome") was the symbolic centre of the city from which, and to which, all distances in Ancient Rome were measured. It was situated in the Roman Forum. Originally covered in marble, the Umbilicus is now a forlorn-looking brick core some 2 metres high and 4.45 metres in diameter.