St. Peter's Basilica historical timeline

A church built on top of a church, over a hundred and twenty years, by architects who kept dying before it was finished.

Chronology

1. c. 320 — the Emperor Constantine raises the first Basilica of St Peter, which Turismo Roma notes was a building of dimensions comparable to the present one. Structural impact: the site is committed to a very large church, and the position of the altar is fixed for all time. What you see today: the footprint, and the reason the high altar stands where it does.
2. From the mid-15th century — the decision is taken to rebuild, and the work runs for approximately two hundred years with contributions from Bramante, Michelangelo and Bernini. Structural impact: no single design governs; each generation inherits and argues with the last. What you see today: a building whose seams are visible if you know where to look.
3. 18 April 1506 — construction of the present basilica begins. Structural impact: Constantine's church comes down as the new one goes up around it. What you see today: everything above ground.
4. 1588-89 — Michelangelo's dome is completed by Della Porta and Fontana, after his death. Structural impact: the crossing is closed and the Roman skyline acquires its fixed point. What you see today: the dome, raised by other men to his drawings.
5. 17th century — Maderno designs the facade, 115 metres long, and the nave is extended to a Latin cross. Structural impact: the plan stops being centralised; the dome is pushed back behind a tall front. What you see today: the processional nave — and the reason the dome disappears as you approach across the piazza.
6. 18 November 1626 — the basilica is completed, a hundred and twenty years after the first stone. Structural impact: the fabric is finished. What you see today: the largest church in the world by interior measure.
7. After completion — Bernini supplies the fittings and the piazza, including the bronze baldachin over the papal altar with its Barberini bees. Structural impact: the interior acquires the single object large enough to hold the crossing. What you see today: the baldachin, and the colonnade outside.

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