San Biagio, Montepulciano site features

The church stands alone below the walls of Montepulciano, in open fields, with nothing built against it — and that isolation is the first and most important thing about it, because it means you can walk the whole way round.

The plan is a Greek cross: four arms of equal length, with a central dome carried on a drum rising over the crossing. The side opposite the entrance has a semi-circular apse, the one departure from perfect symmetry in the plan itself.

Everything outside is travertine slabs, pale and finely jointed, which is why the building changes colour so completely with the light.

Look at the main façade, then look at the two side ones: the same scheme is repeated on all three, with only minor changes. That repetition is the whole point of a centrally planned church — no principal front, because every side is a front.

Each face is divided into two sectors by a large entablature carrying a frieze with triglyphs and metopes, and that frieze runs round the entire perimeter of the building, tying the four arms into one object. Below the entablature sits the portal, with the foundation date cut into it. Above the portal is a window, and over that a triangular pediment with a circular oculus at its centre.

Then the asymmetry. The façade is flanked by a bell tower of several floors, carrying numerous decorative elements and finishing in a pyramidal cusp. On the other side there is nothing. The design included two symmetrical towers and only one was built, so a building conceived as perfectly balanced stands permanently one-sided — the most honest thing on the site, and visible from a mile away.

• The Greek cross central plan — four equal arms under a central dome on a drum, with a semi-circular apse on the side opposite the entrance: the great theoretical form of Renaissance architecture, realised.
• The free-standing setting — outside the walls in open country, with nothing abutting it, so the design can be read from all four sides. Almost no other building in this lineage can be.
• The repeated façade scheme — the main front's composition is repeated, with minor changes, on both side fronts, because a centrally planned church has no single principal face.
• The perimeter frieze — a large entablature with a frieze of triglyphs and metopes running round the entire building, binding the four arms into one volume.
• The portal with the foundation date — cut into the portal itself, in the lower sector of the façade.
• The window, pediment and oculus — stacked above the portal: a window, then a triangular pediment with a circular oculus at its centre.
• The travertine — the entire exterior is formed of travertine slabs, which is why the building turns gold in late light.
• The single bell tower — multi-floored, richly detailed, ending in a pyramidal cusp. Two symmetrical towers were designed and only one built, which is the building's defining accident.