Siena Geography, Climate & Nature

A clay city on clay ridges

Siena stands at 322 metres in central Tuscany, spread across a set of ridges that meet near the centre — which is why the city divides naturally into three terzi and why almost every walk inside it is up or down. The municipality covers 118.53 km². The ground is clay, and that single material explains both the colour of the city and the look of the country around it.

The Crete Senesi

South-east of the city the land becomes the Crete Senesi — literally the clays of Siena. The grey clay is called mattaione, and it is the sediment of a Pliocene sea that covered this area between 2.5 and 4.5 million years ago. Its colour gives a landscape routinely described as lunar: bare, gently rolling hills with solitary oaks and cypresses, isolated farms on the ridge tops, patches of wood, and rainwater ponds called fontoni in the valleys.

Because clay is unstable, erosion has cut it into two characteristic forms: badlands, the bare gullied slopes, and biancane, pale clay domes left standing as the ground around them washes away. The five comuni of the Crete Senesi are Asciano, Buonconvento, Monteroni d'Arbia, Rapolano Terme and San Giovanni d'Asso, and nearby lies the semi-arid Accona Desert.

Chianti on the other side

North-east of Siena the character changes completely. The Chianti hills are higher, wooded and cooler, and they carry vineyards rather than bare clay. Siena sits on the boundary between the two, which is the reason it is the natural base for southern Tuscany: two entirely different landscapes begin at opposite edges of the same city.

A city that has not grown

The municipality holds 53,180 people, the twelfth-largest in Tuscany. The figure matters because the city held about 50,000 before the Black Death of 1348 — so Siena occupies essentially the same footprint it did seven centuries ago, which is the real reason its medieval fabric is intact.

Mediterranean, but at altitude

Siena has a Mediterranean climate modified by sitting at 322 metres on an inland hill, which makes it noticeably cooler than coastal or low-lying Tuscany. Annual rainfall is around 823 mm. August averages 24.4°C and January 6.4°C — and that January figure is the one visitors get wrong, because they arrive dressed for Tuscany rather than for a hill town.

What the seasons do to the landscape

The clay around Siena changes colour through the year more dramatically than most Italian countryside, and this is a genuine factor in when to come. In spring the Crete Senesi are green and sown. By July the crop is off and the clay burns to grey-gold and bare, which is the image most people have of the area without realising it is a seasonal state. After the autumn rain the ground is ploughed and dark.

Season by season

• Spring — the best conditions in the city and the greenest landscape. May is the strongest month.
• Summer — hot and crowded, and the Palio dominates the first days of July and the middle of August. The hill position keeps the nights more comfortable than Florence's.
• Autumn — the best light of the year over the Crete Senesi, the harvest and new oil, and the crowd gone. Arguably the best time overall.
• Winter — genuinely cold, often grey, and very quiet, with monuments on reduced hours.

What to pack for

Warmer clothes than Tuscany suggests in winter, and layers in the shoulder months — a hill at this altitude loses heat fast after sunset. Sun protection and water in summer, since the city's stone and brick hold the heat and the streets are steep. Shoes that handle brick paving on a slope matter here more than almost anywhere.

An agricultural landscape, not a protected one

It is worth being straightforward about this, because Siena is unusual among the cities in this region: it has no national or regional park on its doorstep. What surrounds it is a cultivated clay landscape of considerable geological interest and no protected status. That is the honest position, and it is different from Bologna, which has a UNESCO karst in its hills, or Pisa, which has 23,000 hectares of Ramsar wetland on its western edge.

What the Crete Senesi actually are

The interest here is geological and agricultural rather than wild. The Crete Senesi are the exposed bed of a Pliocene sea — grey clay called mattaione, deposited between 2.5 and 4.5 million years ago and now eroding. Clay holds water badly and vegetation poorly, so the land has weathered into badlands and biancane, pale domes left standing as the surrounding ground is stripped. Nearby is the semi-arid Accona Desert.

The living cover is sparse and highly characteristic: bare rolling hills, solitary oaks and cypresses, isolated farms along the ridge tops, patches of woodland in the folds, and rainwater ponds the locals call fontoni in the valleys. Those ponds are the only standing fresh water across much of it, which makes them disproportionately important.

Chianti, which is the opposite

North-east of the city the Chianti hills are higher, wetter and wooded — oak and chestnut, with vineyards on the cleared slopes. Between them the two landscapes give Siena access to genuinely different habitats within half an hour in opposite directions, even though neither is formally protected.

Inside the walls

Siena's historic centre is brick and stone with very little green, by medieval design. The exception is the Orto Botanico and the gardens that occupy the steep ground inside the walls where building was impractical — which is the same reason the city has sudden views of open countryside from inside its own streets.

A worked landscape, and what lives in it

The country around Siena is farmed clay rather than wilderness, and the realistic expectation should be set accordingly: this is a landscape of field margins, hedgerow, scattered oak and cypress, isolated woodland and rainwater ponds, not of large protected habitat. There is no park authority here to run guided wildlife visits the way there is at Bologna's gypsum hills or Pisa's coastal wetland.

What that structure supports is the fauna of a Mediterranean agricultural mosaic. The fontoni, the rainwater ponds in the valley bottoms, matter more than their size suggests, because across much of the Crete Senesi they are the only standing fresh water — which concentrates everything that needs it.

The woodland, which is where the interest is

The Chianti hills north-east of the city are the better direction for anyone who wants trees and the things that live in them: oak and chestnut woodland on higher, wetter ground than the clay can support. Tuscan woodland of that type carries wild boar in numbers, and they are a working agricultural problem as much as a wildlife attraction.

Birds over open clay

Open, lightly vegetated farmland with scattered trees is raptor country, and the Crete Senesi read exactly that way from the road: long sight lines, bare ridges, isolated perches. It is worth saying plainly that the sources used for this page name no individual species for the area, so none is listed here.

A realistic expectation

Nobody should come to Siena for wildlife, and the page should not pretend otherwise. What the landscape is genuinely exceptional at is being looked at: the combination of bare clay, ridge-top farms and single cypresses is among the most photographed countryside in Europe, and the autumn light over it is the reason. Treat the Crete Senesi as geology and landscape rather than as a nature reserve, because that is what they are.