This network of underground galleries in Rome started at the tomb of Domitilla, the niece of the Emperor Domitian (81-96). In 95, Flavius Clemens, Domitilla's husband, was denounced for his Christian faith (the official charge was 'atheism') and martyred on Domitian's orders. Domitilla was exiled to the island of Pandataria (Ponza) and there, towards the end of the 4th century, according to St Jerome, the cells were venerated where the saint suffered her long martyrdom.

The catacombs became a point of Christian pilgrimage in the 4th century, when a Basilica was built over the tombs of St Nereus and St Achilleus, two martyr soldiers, honoured by Pope Damasus (366-384) with a beautiful epigram that can be read at the entrance which tells the conversion story: they were officials at the court of a persecutor of Christians; they were suddenly transformed by grace, threw down their weapons and joyfully faced martyrdom for Christ. They were probably victims of the persecution ordered by the Emperor Diocletian in 303.

Domitilla's catacombs were lost and only rediscovered in the 16th century, by Antonio Bosio.

The items of greatest interest in the catacombs are: the Basilica of St Nereus and St Achilleus, where some of the original construction still remains; the Cubicle of Veneranda, a good example of Christian piety in the 4th century (it was a great honour for the faithful to be buried near a saint's grave and, in this case, Veneranda wished to be buried next to St Petronilla); the Flavian Vestibule, which is one of the oldest areas in these catacombs (2nd century); and the Flaviano-Aurelian Hypogeum, an example of the decoration used by the first Christians in sacred places.

Early Christian symbols

The catacombs of Domitilla are rich in Palaeochristian art and symbols. Lining the walls of the basilica and the galleries in the catacombs are many signs carved into the walls of the tombs, which refer to the faith of the deceased. Among the Christian markings are:

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  The Good Shepherd: a shepherd carrying a sheep on his shoulders; this is a symbol of Christ the Saviour.
  
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  The fish: an early Christian symbol. The letters of the Greek word for fish (ichthyus) formed the initial letters of each word in the phrase 'Jesus Christ Son of God Saviour'.
  
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  The two letter monogram in Greek X (chi) and R (ro): these form the first letters of Christ's name in Greek (Christos). This monogram is found from the beginning of the Constantinian era (from 312).
  
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  The dove with an olive branch: the symbol of peace.
  
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  The anchor: this is a symbol hidden in the Cross (itself the symbol of salvation), denoting the arrival of the soul in the harbour of the eternal life.
  

The catacombs also contain other figures representing episodes from the Old and New Testaments:

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  Noah and the Ark;
  
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  Moses making water spring from a rock;
  
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  Jonah and the whale;
  
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  Daniel in the lions' den;
  
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  The Birth of Jesus with the three magi;
  
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  Some of Jesus' miracles as related in the Gospels, the favourites being the multiplication of the bread and fishes and the raising of Lazarus from the dead.
  

In the Flaviano-Aurelian Hypogeum there are frescoes, badly faded today, depicting scenes from the lives of Daniel and Moses in the Old Testament.

The Twelve Apostles are represented five times inside the Catacombs of Domitilla, always around Christ seated on a throne and teaching them.

As with all Palaeochristian art, these symbols and paintings are persuasive evidence of the continuity of belief in the Church from the most ancient of days. All the scenes and markings are recognisable in terms of the accepted canon of Scripture, with both Old and New Testaments well represented. None appear to be derived from the Gnostic literature.