Two faces and a door that stayed open
JANUS had two faces, one looking forward and one looking back, and no Greek god matches him at all. He was the god of doorways, gates and beginnings, and January still carries his name. His shrine in the Roman Forum had doors that stood open whenever Rome was at war and were shut only when it was at peace.
Rome was nearly always at war. The emperor Augustus boasted that the doors had been closed only twice in the whole history of the city before him — and three times while he ruled, a record he made sure went into the official account of his achievements.
VESTA was another goddess the Romans did not borrow from anyone. Her round temple held a sacred fire that was never supposed to go out, tended by six priestesses, the Vestal Virgins, who each served for thirty years. If the flame died, it was taken as a warning that the gods were displeased with the whole city.
Borrowed gods that didn't quite fit
As Rome came into contact with Greek culture, it matched its own gods to the Greek ones: JUPITER with Zeus, JUNO with Hera, NEPTUNE with Poseidon, MINERVA with Athena. The stories came across too, and Roman poets happily retold Greek myths with Latin names in them. APOLLO arrived without changing his name at all.
The matches were rarely exact. The Greeks had little love for Ares — in Homer's Iliad even his father, Zeus, calls him the most hateful of the gods. His Roman match, MARS, was one of the most respected gods in Rome: a guardian of farmland as well as of war, and the god who gave his name to March. Rome went on to do the same with everybody else's gods. Wherever the army went, local gods were paired with Roman ones, and a British goddess of healing springs called Sulis ended up sharing a temple at Bath with MINERVA.
Raised by a wolf, founded in a quarrel
Rome's founding story belonged to nobody else. The twins ROMULUS and REMUS, sons of MARS, were left by the River Tiber as babies and fed by a she-wolf until a shepherd took them in. Grown up, they set out to build a city and argued about where; the quarrel ended with REMUS dead and the city named after his brother. Nor was that the end of it — ROMULUS was said to have vanished in a sudden storm and become the god QUIRINUS, so the Romans ended up worshipping their own first king.
Roman historians later worked out a birthday for the city, 21 April 753 BC, and Rome still celebrates it every April with parades in Roman costume. A bronze she-wolf feeding the twins is the city's emblem, though scientific dating suggests the famous statue in Rome's Capitoline Museums was cast in the Middle Ages, and the twins were only added in the 1400s. For the city's real history, from the Republic to the emperors, see our Ancient Rome puzzle.