This monumental porphyry sarchophagus is thought to be that of St. Helena, the mother of Constantine.
It dates from the time of her death in335 AD and came from the Imperial mausoleum near Rome.
It is carved with military scenes and men on horseback,which makes it debatable as to whether it actually held
the remains of Helena, or that of her husband Constantius or possibly Constantine himself.

Helena, the mother of Constantine, is said to have gone to the Holy Land to look for the "true cross" on which
Christ was crucified;
Helena is honored in St. Peters with a large sculpture in a niche in one of the enormous piers at the crossing,
showing Helena holding the cross for which she searched.

The sarcophagus was brought to the Vatican in the late 18th c.