The catacombs of Domitilla, close to the Appian Way, have been restored using laser technology to remove centuries of grime and dirt that had rendered them invisible.
The renovated areas include frescoes from both pagan mythology and Christian faith, revealing how wealthy Romans moved away from their pagan beliefs toward the religion of Christ around the fourth century AD.
The Domitilla catacombs, named after a member of the Roman family that had commissioned the burial grounds, are the largest in Rome.
They stretch over 12 kilometres (7.4 miles) and descend four levels with 26,250 tombs, dating from the second to the fifth centuries.
The intricately painted frescoes decorate the ceilings of two crypts, which were both unveiled on Tuesday after decades of delays to renovations.
They depict scenes of from the Old and New Testaments, including Noah and his Ark and Jesus's feeding of the 5,000 with bread and fishes.
There are also peacocks shown in the paintings - a pagan sign of the afterlife.
At the centre of the ceiling fresco is an image of Christ with two men either side of him, believed to be St Peter and St Paul or St Nerius and St Achilleus.