Yerevan is a capital made of a single stone.

01 The stone comes from a volcano

Tuff is a rock of volcanic origin, light, easy to cut and surprisingly durable. In the mountains ringing the valley it is quarried in a wide range of tones: pink, ochre, cream, grey, black, and a series of reds running from salmon to wine. It is cheap to work, hard to imitate, and it was to hand.

That geological detail is what decides the city's appearance, and also what explains why the colour changes with the hour. Mid-morning the façades lean pale pink; late in the afternoon, with the sun low and the roughly thousand-metre altitude clearing the air, the same stone turns orange and almost red.

02 1924: one plan and one material

The second piece is a date. In 1924 the architect Alexander Tamanian signed the master plan that turned a provincial capital into a modern city. He replaced the old fabric with a radial-concentric structure —a circular core with wide avenues running off it— interleaved with green space, and proposed that everything be built in pink tuff.

The heart of that plan is Republic Square: 3.5 hectares, with an oval measuring 230 by 110 metres and a central paving pattern drawn from an Armenian carpet. It is not an inherited square that took shape over time: it is a piece designed in one go, with the buildings that enclose it conceived as an ensemble.

03 Looking closely at a façade

Here is the recommendation that changes the visit most, and it costs nothing: walk up to one of the square's façades and look at it from a metre away. From a distance they seem to be one colour; close up you see they are built from blocks of different tones laid in a chequer, alternating pink, cream, ochre and grey.

And there is a second layer. On top of that chequered base the stone is carved: friezes with geometric and vegetal motifs, worked capitals, bands running along the arches. It is an ornamental vocabulary taken from medieval Armenian architecture and applied to buildings of the thirties and forties. That mix of modern plan and ancient ornament is exactly what defines the city.

04 The stairway up to the viewpoint

The other piece to walk is the Cascade, a monumental stairway clad in pale stone that climbs from the centre to the hill to the north. It works simultaneously as a staircase, a stepped viewpoint and an open-air museum: there are sculptures on the terraces, and a succession of escalators runs up inside it.

Climbing to the top on foot takes about twenty minutes and is worth doing late in the afternoon, when the stone takes on colour. From the upper terraces you see the 1924 plan laid out below: the radial avenues, the green ring and the regular grid of roofs, all in the same tone.

05 What Yerevan leaves you

What stays with you is a visual coherence that hardly exists any more in Europe. Here you do not have to hunt for the old town among modern blocks or tell the layers apart: the whole city is one colour, and that unity comes not from an aesthetic regulation but from a practical decision taken a century ago about which stone to use.

And an uncomfortable idea stays about what an ancient city means. This place has been inhabited for more than two thousand eight hundred years and almost nothing you see is a hundred years old. The antiquity is underneath, in the name and in the hills; what you walk is a twentieth-century city built from the stone of an extinct volcano.