The Ludovisi Sarcophagus

So named from its first owner after rediscovery - Ludovico Ludovisi - and currently to be seen in the Palazzo Altemps, a short walk away from Piazza Navona.
It dates from the mid 3rd Century AD, and is believed to have been intended for Gaius Valens Hostilianus - a son of the short-lived Emperor Decius (ruled 249 - 251).
Hostilian is seen top centre, without a helmet. His outstretched arm represents both leadership and victory. The young man has an "X" on his forehead - which was a sign that he was a follower of the god Mithras, who was very popular with soldiers at this time.
The sarcophagus was found in 1621 on the Via Tiburtina, which runs NE out of Rome.
Hostilian is depicted on the sarcophagus engaged in battle against the Goths, but he was not destined to follow the fate of his father and brother.
Decius and his eldest son, Herrenius Etruscus - who co-ruled with his father - were both killed at the Battle of Abritus, in what is now Bulgaria. He was the first Roman Emperor to die in battle against a foreign enemy.
Hostilian, who became Emperor himself very briefly in 251 AD, died from the plague.
Decius' short reign was most notable for a resumption in persecutions of groups who refused to sacrifice to the Emperor. Though they weren't the only ones targeted, a large number of Christians met their deaths - including Pope Fabian in 250. Decius built a bath complex on the Aventine, the ruins of which survived until the 16th Century, and he is recorded as having repaired the Colosseum when it was struck by lightning.
This is a late example of this type of sarcophagus. Ornately carved "battle" sarcophagi were at their most popular c. 190 - 210AD.