In Istria the ground changes colour three times
Geologists divide the peninsula into white, grey and red Istria: bare limestone in the mountains, marl and sandstone in the centre, red earth on the coastal plateau. The hilltop towns, the valley truffles and the river that vanishes beneath a castle all come out of that same division.
Almost everyone reaches Istria by the coast and stays there. From the shore the peninsula looks like a coastline of fishing towns with a green filler behind it. Head a little way inland and the ground changes: the red earth of the olive groves gives way to soft grey hills, and in the background rises a bare, whitish range.
Those three shifts are not scenery. Each colour is a different rock, each rock treats water in its own way and, from there, people have built differently in each band. Istria is not a coast with a hinterland: it is three soils laid side by side.
01 White, grey and red
White Istria is the high north-eastern band: the Učka massif and the Ćićarija range, made of heavily karstified Cretaceous and Palaeogene limestone. The roof of the peninsula is here, Vojak, at 1,401 metres. The nature park protecting the massif covers 160 square kilometres of rock, forest and limestone walls.
Grey Istria fills the centre. It is a depression filled with flysch, an alternation of marl, sandstone and thin limestone beds that breaks down easily and forms rounded hills. It is the landscape of ridges, open valleys and perched towns that most people associate with the interior.
Red Istria is the west and south-west: a plateau of Jurassic and Cretaceous carbonate rock covered in terra rossa, the iron-rich reddish clay left behind when limestone dissolves. It is the coastal band, and it is the one nearly everyone sees first.
02 Why the towns are up high
The most repeated image of the interior is a walled town on top of a ridge. It is not a coincidence of two or three places: it is the pattern of the whole grey band. Motovun sits some 270 metres up above the Mirna valley; Hum at 349; Grožnjan on another crest a few kilometres away. From any of them you can see the next.
The reasons given for that position are three, and they recur: defence against whoever came up from the coast, malaria-free air above the marshy valley floors, and a view over the routes linking the Adriatic with the interior. All three depend on the same trait: flysch forms narrow crests separated by wide, damp valleys, so there was an obvious place to live and an obvious place not to.
The result is a very small scale. In the 2021 census, the settlement of Motovun had 397 inhabitants; Grožnjan, 142; Hum, which bills itself as one of the smallest towns in the world and appears in documents from 1102, had 52. These are towns that fit into a single street and a wall, and that you can walk end to end in the time it takes to drink a coffee.
That scale has allowed unexpected uses. In 1965 Grožnjan began handing empty houses to artists and, since 1969, it has hosted an international music youth centre. Today it has around twenty galleries in a settlement of fewer than a hundred and fifty residents. Motovun, for its part, has filled its slopes every summer since 1999 with a film festival. Not much more than that fits on top of a flysch ridge, and perhaps that is why it works.
03 What grows in the damp valley floor
Climb onto the walls of Motovun and look down, and you see the other side of the pattern. The valley floor is flat, the Mirna runs straight in its channel, and across it lies a compact forest of some ten square kilometres, 280 hectares of which are specially protected.
That damp valley-floor forest is the ground of the Istrian white and black truffle, hunted with trained dogs. Here, near Livade, on 2 November 1999, a white truffle weighing 1.31 kilos was found and recorded by Guinness as the largest in the world. Its finder had it cast in bronze and ate the original at a dinner for around a hundred guests.
What matters is not the record but the geography it reveals. The same valley floor that the towns avoided for centuries as unhealthy is the one that now supports the region's most expensive product. Crest and valley do not compete: they are two halves of one rock.
04 Where grey meets white
There is one place where the division can be taken in at a glance. The Pazinčica rises and flows over grey flysch, which is impermeable, so the water runs on the surface like any river. At Pazin it reaches the limestone, which dissolves, and disappears underground through an abyss some hundred metres deep that opens right beneath the castle.
The abyss cannot swallow the river in full flood. In 1896 the water rose until it was only 30 metres below the castle walls, and there were smaller floods in 1964 and 1993. The water does not re-emerge on the west coast, as was once assumed, but to the east and south, along the Raša valley.
Jules Verne never came here, but working from a friend's descriptions he had the hero of Mathias Sandorf, published in 1885, escape through this gorge. It is easy to see why it served him: a river vanishing into the rock beneath a fortress looks like an invention, and it is simply the exact point where grey Istria ends.
05 A ground that lets water through
Heading down to the south-west, the earth turns red and the landscape flattens. Terra rossa did not end up there by chance: it is what remains when rain dissolves limestone over a long time and carries the carbonate away. The iron-rich clay left over is what stains the fields.
That same limestone changes the relationship with water. In the grey band rivers run on the surface and waterlog the valley floors; in the red band rain soaks through the rock instead of running over it. So there are no damp valleys to avoid and no reason to perch: the towns of the plateau and the coast spread out on the flat, and farming here means olives and vines on red ground. Even the dry-stone huts dotting the fields come out of that stony, limestone-laced earth.
It is the interior's principle read backwards. In grey Istria the water stays and people climb; in red Istria the water leaves and people stay low. The coast that nearly everyone takes for the whole of Istria is, in fact, the band where the rock lets the water through.
06 How to travel it
The first decision is to cross the peninsula instead of skirting it. A drive from the west coast towards Učka runs through all three bands in a single day, and the change of colour shows in the road cuttings, the ploughed fields and the stone of the houses.
The second is to look down from each high town. The walls of Motovun, the viewpoint at Grožnjan or the rim of the Pazin abyss make sense because of what lies below: the damp valley, the truffle forest, the place where the river leaves.
And the third is a simple habit: notice the mud on your shoes. Red near the sea, grey among the hills, white dust in the mountains. In few places does the ground tell you so plainly which part of the territory you are in.
