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Ambrogio Lorenzetti’s Allegory of Good and Bad Government (1338), the greatest secular medieval fresco cycle in Europe, decorates the old city council chamber.

This work of 1330 is Simone Martini’s greatest – though some challenge its authorship. The austere Maremma landscape, where Guidoriccio has just quashed a rebellion, is charming.

The square’s nine sections honour the medieval ruling Council of Nine. Its fountain and slope are more than decorative: they’re integral to the city’s water system.

One of the tallest medieval towers in Italy, at 102 m (336 ft). There are 503 steps to the top – worth the effort for the stunning view.

When the Black Death of 1348 finally abated, the third of Sienese citizens who survived built this marble loggia to give thanks for their deliverance – and to pray against a repeat of the plague. A detail of its pretty stone carving is illustrated here.

The felicitous “Fountain of Joy” is pretty enough, but it is merely a mediocre 19th-century reproduction of the original, whose weathered carvings by Jacopo della Quercia are preserved in the Museo Civico (see Siena’s Museo Civico).

The city’s civic palace (1297–1310;), with its graceful brickwork, Gothic three-light windows and thoroughly medieval crenellations, set the standard for Sienese architecture. Its sumptuously decorated rooms are now part of the civic museum.

A commercial tribunal once held court under this 1417 loggia decorated with statues by Vecchietta and Federighi. The judges were so famously impartial that governments from across Europe brought their financial disputes to be heard here.

Housed in Siena’s only Florentine Renaissance palazzo are the Tavolette di Biccherna – municipal ledgers from the 13th century, with covers by Sano di Pietro, Ambrogio Lorenzetti, Domenico Beccafumi and others.

The oldest building on the Campo; its curving 13th-century façade set the style for the rest of the square.