Between about 1782-85, the great French landscape painter Pierre-Henri de Valenciennes (1750–1819) built his personal library of oil sketches of the countryside around the city of Rome. He then returned to France, where he assembled them into finished paintings in his studio.

A Capriccio of Rome with the Finish of a Marathon from 1788 is a direct descendant from the pioneering landscapes of Nicolas Poussin of more than a century earlier. Groups of figures at the left and right are watching athletes run in to the finish of their race. Behind them is a town based on passages of Roman architecture, but isn’t recognisably a depiction of Rome. This is an intermediate between the completely idealised landscapes of Poussin, and later topographically accurate views.

Valenciennes then wrote up this technique of sketching in oils in front of the motif in his influential manual on landscape painting published in 1800. This remained the standard work well into the twentieth century, and was used by Impressionists including Paul Cézanne. Most budding landscape artists travelled across Europe to train in the Campagna during their formative years.

Achille Etna Michallon was one of the earlier visitors in about 1817-19, when he painted the spectacular scenery of Tivoli, shown here with a Goatherd Opposite the Falls of Tivoli. These waterfalls are more painterly than his early realism.

Michallon’s unusual View of Santa Scolastica in Subiaco from 1818 shows this famous Benedictine monastery in Subiaco, Lazio, dedicated to the sister of Saint Benedict of Nursia.

Carl Blechen studied at the Berlin Academy from 1822, then travelled to Dresden and Switzerland. After he was dismissed as a stage painter at the Royal Theatre in Berlin in 1827, he travelled first to the Baltic coast then south to Italy, where he too painted plein air in the Roman Campagna. His copious oil studies were in a similar style to those being painted in the early nineteenth century by others in the area, but back in Berlin were seen as being radically different.

Camille Corot was perhaps the first major landscape painter both to follow Valenciennes’ teaching and to show his sketches in public. During his first stay in Italy between 1825-28, he developed his skills painting outdoors in the Campagna, producing classics such as his View of the Convent of S. Onofrio on the Janiculum, Rome above, and The Bridge at Narni below.

Heinrich Bürkel’s Shepherds in the Roman Campagna from 1837 has an almost documentary quality, in the rough and dusty peasants slumped on their horses and donkeys. In the foreground a couple of ewes are looking up at their lambs being carried in a pannier, and a dog is challenging a snake by the roadside.

In 1850, the twenty-two year-old Swiss artist Arnold Böcklin moved to Rome, where he too started painting in the Campagna.

In the Alban Hills from 1851 is a fine depiction of these hills about 20 km (12 miles) south-east of the city of Rome. Unlike many artists working in the Campagna at the time, Böcklin must have painted this work in the studio from extensive sketches and studies made in front of the motif. Look closely, though, and there’s a dark figure standing beside a small smoking fire, to the left of the central mass of trees, and further to the left might be the entrance to a dark cavern.

Böcklin uses more dramatic lighting in this Roman Landscape from 1852. Its dark wood is very dark indeed, not the sort of place to enter alone. At the foot of the prominent tree at the right is what appears to be a woman undressing, as if going to bathe in the stygian gloom.

Nils Jakob Blommér’s undated Landscape from Italy is another plein air oil sketch of the Roman Campagna in the tradition of Valenciennes.

In the middle of the nineteenth century, the young French Impressionists broke new ground by applying Valenciennes’ teaching to plein air sketches they made in the countryside around Paris, and on the north coast of France. They then exhibited those sketches as finished works, the working method of Impressionism.

The countryside around the city of Rome has played a vital role in the history of landscape painting. For nearly a century, from the 1780s until the development of Impressionism, painting oil sketches in this area became a mandatory phase in the training of all good landscape painters in Europe. This weekend I show some of the best examples of these exercises undertaken early in the careers of some of the greatest artists of the nineteenth century, from Valenciennes who started it, to Corot and Böcklin.

It was the co-founders of landscape painting in Europe, Nicolas Poussin (1594-1665) and Claude Lorrain (c 1600-1682), who started painting the Roman Campagna, from about 1624 onwards. Although both were born in France, they spent almost their whole careers based in Rome, where they went out and sketched in front of the motif. They then used those studies to assemble composite idealised landscapes for their studio oil paintings, leaving little trace of their original sketches.

It was Claude Joseph Vernet (1714-1789), another pioneer French landscape artist who worked for many years in Rome, who first recommended to the young Pierre-Henri de Valenciennes (1750–1819) that he should follow this practice by painting oil sketches en plein air in the Campagna. In about 1782 Valenciennes started to amass his personal image library of sketches of the Roman countryside, and when he returned to France in 1785 he used those for his studio paintings.

One of the finest and the best-known of all Valenciennes’ oil sketches is this showing Farm-buildings at the Villa Farnese: the Two Poplar Trees reputedly from an earlier visit in 1780. This shows a Renaissance villa now in the centre of the city of Rome, although here its park setting makes it look as if it is out in the country. It was built in 1506-10 for a banker, and appropriately contains superb frescoes by Raphael and others. It is now owned by the state and most is open to visitors.

View of the Convent of Ara Coeli with Pines is a superb view of what’s known as the Basilica di Santa Maria in Aracoeli, again in central Rome. This is on the top of the Campidoglio, and affords the view over the city appearing behind the pine on the right. It’s situated close to the Forum.

This untitled sketch shows a different view over the city.

Several of these surviving oil sketches are brilliant studies in the effects of light, such as Rome: Houses and a Domed Church above.

I’m not sure if anyone has identified the buildings shown in Rooftops in the Shadows, but suspect that this too is close to the centre of Rome, perhaps on one of its hills. Is this the first plein air painting of washing on the line?

Around forty years later, John Constable sketched clouds and weather in what he called ‘skying’. Here’s one of Valenciennes’ groundbreaking sketches from the early 1780s, in Rome: Study of Clouds. He wasn’t the first plein air painter by any means, nor the first to make sky studies, but it was he who established the practice among landscape artists, both in his direct teaching and in his book published in 1800.

The Louvre has most of Valenciennes’ surviving oil sketches, but by no means all of them. This superb Italian Landscape is now in the Museum Boijmans Van Beuningen in Rotterdam, The Netherlands.

The National Gallery of Art in Washington, DC, has another of his sky sketches, this Study of Clouds over the Roman Campagna.

The Cleveland Museum of Art, in Ohio, has this magnificent View of Rome, which I think compares with the Villa Farnese above in its quality. Notable here is the depiction of the clouds of dust and smoke rising from the streets of the city, which surely qualify it as an ‘impression’.