[1] Constructed during the second and third centuries, this labyrinth of underground passages contains frescoes and a wealth of Christian iconography while also presenting masterful engineering skills and innovative architectural techniques.

[3] The first region includes the Cubicle of Ampliato, which belonged to a family of imperial freedmen who had dug the hypogeum; this vast environment is separated into two sections by an arch used to support a landslide vault.

[6] Although her remains were removed from Domitilla and moved to the Vatican at the insistence of the Frankish king, it is believed that the cult of Petronilla was celebrated in the underground basilica of Nereus and Achilleus, relating her hagiography to their Passions.

[6] Inside the Catacombs of Domitilla are images, some of which were revealed by the restoration, reflecting the life of bakers,[7] grape vines, Jesus with the apostles, Noah's ark, and Daniel with the lions.

[7] Other biblical figures in the various cubicula include the Virgin Mary with child,[8] Adam, Eve, Jonah, The Good Shepherd, a young man dressed as a cardinal with apostles Peter and Paul.

[9] Non-biblical, or pagan, figures include representations of Spring and Summer in the form of females with wings, both pictured with attendants[9] and scenes depicting Orpheus[10] surrounded by birds, beasts and the sheep that typically accompany him.

[13] The corridor of the cubicle was revealed to be garnished with coffered ceilings and interior decorations, including a reproduction series of opus sectile on the hoof of the inner curve of the four arcosolia depicting painted scenes of the Prophet Jonah.

[13] Frescoes of four biblical scenes are depicted on the walls of the corridor, including the Binding of Isaac and Noah, as well as Jesus in multiplication of loaves and the miracle water from the rock.

[13] Dating back to the end of the second century and the oldest nucleus of the site, the Flavian Hypogeum is composed of a large gallery featuring four niches that host the sarcophagi homing the most important members of the family.

[20] Two frescoes commemorating the city's early Christian roots have been exposed thanks to a seven-year restoration project, using laser instruments to burn away chalky deposits, algae, and residual smoke from oil lamps.

[21] Scenes depicting Old and New Testament figures, likely commissioned 1,600 years ago, emerged from the debris and pollution and provided useful context to the transition period from Paganism to Christianity.