Basilica of Santa Prassede historical timeline

A pope emptied the catacombs into this church, and decorated it for his mother.

Chronology

1. 817-824 — the reign of Pope Paschal I. Structural impact: the decision is taken to move martyrs' remains out of the catacombs and into churches inside the walls. What you see today: the reason this basilica exists in its present form.
2. Under Paschal I — he digs up numerous skeletons and transplants them to this church from the catacombs. Structural impact: the basilica is enlarged to receive them. What you see today: the porphyry disc in the floor, marking the well where legend says Prassede gathered martyrs' remains and blood.
3. c. 828 — Paschal enlarges and decorates the basilica, hiring a team of professional mosaicists for the apse, the apsidal arch and the triumphal arch. Structural impact: the church acquires the mosaic programme it is known for. What you see today: Jesus between Peter and Paul in the apse, and twelve men on each side of the apsidal arch holding wreaths of victory.
4. Under Paschal I — the Chapel of San Zeno is built as a funerary chapel for his mother Theodora. Structural impact: a small, entirely mosaicked room is added to the right aisle. What you see today: what Turismo Roma calls the most significant Byzantine monument preserved in Rome.
5. 1223 — Cardinal Giovanni Colonna brings the column of the flagellation to Rome as an emissary to the Holy Land. Structural impact: the church gains a relic and a destination for pilgrims. What you see today: the column — with the reference work's caveat that medieval relics of this kind lack indisputable authenticity, there being no forensic evidence.
6. c. 1612 — Bernini carves the bust of Bishop Giovanni Battista Santoni, who had died in 1592. Turismo Roma calls it his first sculptural work. Structural impact: none. What you see today: a funerary monument that is easy to miss and historically outsized.

• Official website
• Wikipedia