Basilica of Santa Cecilia in Trastevere historical timeline

A house, then a title, then a basilica built to hold a body that had been moved twice.

Chronology

1. 222-235 — Cecilia is martyred under Marcus Aurelius Severus Alexander. Structural impact: none yet; the site is a house. What you see today: the Roman rooms under the church, which are what the basilica was built over.
2. Probably 3rd century — the first church is founded by Pope Urban I. Structural impact: a domestic building becomes a place of assembly. What you see today: the footprint, which has not moved.
3. Late 5th century — it is recognised as the Titulus Ceciliae. Structural impact: none. What you see today: the dedication, unbroken since.
4. 822 — Pope Paschal I rebuilds the church and moves Cecilia's relics here from the Catacombs of St Calixtus. Structural impact: the ninth-century basilica is the building the later church is wrapped around. What you see today: the plan, and the reason the altar is where it is.
5. 1293 — Arnolfo di Cambio makes the ciborium. Structural impact: a Gothic canopy over a ninth-century altar. What you see today: it, in the presbytery.
6. c. 1289-1300 — Pietro Cavallini paints the Last Judgement on the counter-facade. Wikipedia gives 1295-1300 in one place and about 1289-93 in another. Structural impact: none; it is painted onto the existing wall. What you see today: the fragment above the nuns' choir, and the colour of the wings.
7. 1599 — the tomb is opened. Structural impact: none. What you see today: a marble slab in the pavement quoting Maderno's sworn statement that he recorded the body as he saw it.
8. 1600 — Stefano Maderno carves the statue beneath the main altar. Structural impact: the focus of the church shifts to the floor under the altar. What you see today: the single most looked-at object in the building.
9. 1900 — the Cavallini frescoes are rediscovered. Structural impact: access to the counter-facade becomes a visit in its own right, through the convent. What you see today: the separate opening hours, which exist because of this.

• Official website
• Wikipedia