Nicolas Poussin (1594-1665): The Nurture of Jupiter c. 1636-7, Oil on canvas 96.2 x 119.6 cm.  Dulwich Picture Gallery

One of the unexpected highlights of the Dulwich Picture Gallery in South London is its remarkable collection of seven pictures by the great seventeenth-century French painter Nicolas Poussin, who passed the whole of his career in Baroque Rome, painting by the light of that very Roman (though originally Umbrian) artist, Raphael.

It was Raphael’s clarity and elegance of composition, as exemplified in his frescoes for the Vatican (and we can see it in his tapestry cartoons at the V & A), that Poussin applied to pictures intended for the homes of his rich patrons – essentially for domestic consumption. (He executed a large altarpiece for St Peter’s but didn’t primarily work for the Church.)

Poussin is in some eyes an austere, cerebral painter who lacks warmth and charm. Certainly there’s an intellectual quality to his work that is central to its power and meaning. But he could invest his serious thoughts with real beauty and, in particular, he was a marvellous colourist. Dulwich possesses a ravishing example, one of the most sensuously coloured of all seventeenth-century paintings.

In his recreation of the infancy of the future king of the gods, Poussin celebrates a foundation myth of Greek culture through very Roman eyes. Like so many of his pictures this one combines figures with landscape, bringing the rhythms of hillsides and tree forms into play with the human body, draped and naked.

All these details contribute to the telling of the story of how the Titan Cronus’s infant son, having been saved by a trick from being devoured by his father, was brought up by shepherds on Mount Ida in Crete, to become the king of all the gods – Zeus, named Jupiter in the Roman pantheon. He was nourished on honey and the milk of the goat Amalthea, one of whose horns later became the Horn of Plenty, miraculously replenished to supply those who needed its sustenance.

Although the setting is obviously an ideal one, Poussin doesn’t idealise the subject, but shows the child suckling at the teats of the goat with an almost shocking, graphic intimacy. The gaze of the child in the right-hand corner seems faintly prurient, focusing as it does on this intimate event. It is also a strong launch-pad for the diagonal that pushes through the whole design in opposition to the sweep of the hillside beyond.

Colour is a crucial element in this poetic mix. The honey-yellow dress of the nymph collecting the honey on which the infant god is fed, the flowing amethyst drapery of the genius of the river pouring its waters from her urn, are colours both symbolic and integral to the natural harmonies of sky and foliage in the surrounding landscape.

But though the theme is the infancy of a god, this is not a meditation on divinity, or power, and their origins. Rather it creates for us an idyllic world, a golden age of innocence, fecundity and natural harmony, presented in terms of a subtly balanced composition of intersecting diagonals echoed in microcosm by the active limbs of the figures who enact the story.

The picture collection at Dulwich is one of the most extraordinary in the country. Unlike other public collections in London – those at Kenwood, Apsley House, or Manchester Square, for instance – it originated not in the private gallery of an aristocrat, but as a commercial project to supply the King of Poland with an authoritative assemblage of masterpieces representing European art from the Renaissance to the eighteenth century: a typically English, entrepreneurial venture. A London dealer, Noel Desenfans, with the help of a Royal Academician, Sir Peter Francis Bourgeois, put it together, but in 1795 war intervened and it never reached King Stanislas II Augustus of Poland whose brother Michael Poniatowski had given Desenfans the commission. (Poland was partitioned.) In 1811 Bourgeois bequeathed the collection to Dulwich College and in 1814 it was placed in a new gallery designed by John Soane, the first building designated as a public picture gallery in the world.

As a potential national collection it measures up pretty well. It contains a number of fine works by major artists: Raphael (yes, indeed), Rembrandt, Rubens, Van Dyck, Guercino, Claude, Cuyp, Murillo, Watteau and many of the little Dutch masters. Important British pictures came with later gifts and bequests. The haphazard way it came into existence seems quintessentially English, and for a long time it was hardly noticed by the public. Now, happily, it is known and celebrated, even in London itself.