‘A Line in Scotland’, a sculpture by Richard Long

Landscape as a site for artistic pleasure began in the late Middle Ages, reached its apogee with the romantics – Constable, Turner, Caspar David Friedrich – and petered out with the end of modernism. It was alien to classical civilisation and is anathema to most contemporary art. So the great revelation of Richard Long’s retrospective at Tate Britain is that here is an artist who, since the 1960s, has been quietly, radically reclaiming landscape as a source of delight, both sensual and intellectual.

This is a sweeping, joyful, dramatically alive show. Long’s seminal idea – that walking became art when he said it was – is demonstrated in different ways: slate circles arranged on specific sites or imported into the gallery; sticks or stones marking intervals on a walk; photographs; text pieces noting times, places and thoughts on his journeys. The idea gains seriousness, credence, occasionally humour, from the repetition and variety of its manifestations. And even if you leave, as I did, unconvinced by every element, the show coheres room by room into a persuasive exploration of man’s relationship with and place in the abstract entity we call nature.

“Heaven” and “Earth”, the mud-and-water frescoes opening the show and providing its title, evoke both the visceral, spontaneous primitivism of cave-painting and a highly ordered vocabulary of abstraction. Derived from ancient Chinese symbols, Long’s marks include signs for mountains, river, wind, tranquillity. “Heaven” is based on six solid lines; “Earth” on six broken ones, denoting the basic sky/earth, cerebral/physical duality at the heart of his work. It is a delicately rendered metaphysical piece, answered by the concluding work, a wall painting in Cornish china clay which, Long says, “represents the force of my hand speed, and the forces of water, chance and gravity”. The clay courses down like summer rain, shaping patterns that suggest cosmic variety, life-giving energy, lyrical affirmation.

Both pieces are rooted in the personal and gestural, with the mud in “Heaven” and “Earth” coming from the Avon in Long’s native Bristol. Throughout the show, the city’s contours of oozing river, mud banks, spring tides, caves, limestone cliffs, together with the flat expanse of nearby Dartmoor, leave an imprint on Long’s work that is as pronounced as Suffolk’s Stour is on Constable. A photograph of a Somerset beach, a text work denoting “A Straight Northward Walk Across Dartmoor”, an Exmoor Ordnance Survey map marked with the route of “A Ten Mile Walk”, as well as photographs recording treks across treeless plateaus in the Alaskan tundra, the Mongolian steppes, the Argentine pampas – all echo or reference these landscapes of Long’s childhood.

Standing out radiantly from them all is “A Line Made By Walking”. In 1967, aged 22, Long took a train from London’s Waterloo, got off at the first station in open countryside, found a field, walked back and forth until he had made a flattened line, waited for sunlight, took a photograph and went home. The rough, grainy image of that sunbeamed line is direct, luminous, mysterious, but also earthy, heavy with the weight of feet trampling grass.

In one stroke, “A Line Made by Walking” challenged what sculpture could be, relocating it from the studio to the world, opening it up to time and space. The piece defined Long’s artistic language: rigorous abstraction – Malevich’s geometric forms and Klee’s “taking a line for a walk” come to mind – and arte povera’s economy of means and materials consolidated into a new way of making art. What follows in Long’s photographic work enriches but doesn’t really advance on it: “England” (1968), recording a cross stomped into a daisy field, is an arresting complement; 20 years later, the tapering diagonal “Dusty Boots Line” replicates its austere formality on the Saharan plain.

Long insists that “if the idea is good, the beauty looks after itself”. Beauty and optimism are the major part of the enjoyment these landscapes deliver: the transcendence of the everyday in the domestic images, man dwarfed by the elements in the mountain or wilderness ones. Only occasionally is a reference more historically specific, as in the superb crystalline diptych “Windmill Hill to Coalbrookdale”, recording a 113-mile walk from a Neolithic Wiltshire site whose inhabitants were the first in England “to make permanent changes to the landscape”, to a Shropshire settlement on the River Severn, marked by an elegant wrought iron bridge stark against misty stream and trees, “the birthplace of the industrial revolution”.

Less satisfying are the overlarge colour prints from the 1990s – formally weak and not altogether distinguishable from tourist snaps. Yet more hard-going are recent pure text pieces, in coloured capitals, which read like sub-Johnny Cash lyrics crossed with travel brochures: “Forest White Butterflies Crossing a Stream/Animal Droppings Slippery Boulders Peat Bog” as a record of a walk on Japan’s Chokai Mountain in 2003; “One New Moon Two Thunderstorms ... Countless Stars The Infinity of Space” from Switzerland in 2004.

Has Long gone decadent? He has always insisted that he is a conceptualist, not a romantic: he came of age in the 1960s when “the idea of filling the world with more and more objects became questionable”, and he studied at St Martins with “living sculptures” Gilbert and George, whose photo- and text-based aesthetic – and later hints of didacticism – this show partly recalls. But Long is significant because he became a realist anyway. Although he often dematerialises the art object, he also depends on real, natural materials and real human-scale actions: walking, lifting, placing, carrying, throwing, marking.

In a museum setting, the most compelling results are the floor sculptures, six of which form this show’s stunning centrepiece. The variations between these deceptively simple works are a delight: a sombre, smooth slate “Stone Line”; a monumental ring of uneven white stone, “Norfolk Flint Circle”, which seems to glow with an inner light; the baroque chromatic play of “Black White Blue Purple Circle”; the formal simplicity of the tightly packed “Basalt Ellipse”.

Of course this is Stonehenge crossed with Carl Andre: English romantic sublime in measured minimalist register. Long is a peculiarly English artist: narrative, naturalistic, modest in the almost reverse imperialism – a remnant of his youth in Bristol, a city with a troubled imperial past? – with which he leaves  the lightest intervention in the most difficult locations. “Circle in the Andes”, “A Line in the Himalayas” are whispering contrasts to the loud theatricality of American land art. Long has, literally, trodden his own road for 40 years, exteriorising an eclectic vision that has become more and more relevant, and that now ripples out with terrific resonance from the local to a timely, timeless, meditation on the fragility and power of the earth.

‘Richard Long, Heaven and Earth’, Tate Britain, London, to September 6. www.tate.org