Eventually the road flattens out into a ledge wide enough to accommodate a few parked cars. The streets of mountain villages like these are too narrow for a vehicle to manoeuvre through with any ease, so most visitors leave their cars at a safe distance and explore on foot. The road continues uphill, opening out into a square. Beneath it, houses tumble down the mountainside, and there are views of the red-tiled roofs below and the sierra beyond, framed by arches of colourful bougainvillea.

Zahara is one of the loveliest of the pueblos blancos, white villages dotted randomly against the more muted shades of the countryside.

Most pueblos in Andalucia are white, but not all are white villages. The reasons for this appear to be complicated, since many share a common history. The pueblos blancos were developed by the Moors who conquered much of Spain from the early 8th century and remained in Andalucia for nearly 800 years.

Fierce battles were fought between the Muslim rulers and the Christian kings who wanted to win them back.

The villages are white because of the limestone wash with which the buildings are painted, used for centuries in preference to any other colour because it absorbs less heat.

Local by-laws prevent the buildings being painted any other colour. Traditionally, it was the task of the woman of the house to repaint the walls, a job that would be done each spring after the rains had gone.

Many of the villages had been settled long before, by the Romans or Phoenicians, but it was the Muslims who gave them their distinctive appearance. Most striking is the street layout: warrens of narrow alleys that dive and curl to accommodate the terrain, since most of the villages are high up in the mountains. The houses are a mixture of grand and simple, built side by side in a random fashion, a feature most noticeable in Arcos de la Frontera. Their windows have broad outside ledges, usually covered with pots of bright flowers and protected by iron grilles. Typically, there is some kind of fortification at the highest point, like the castle in Olvera, which now contains a small museum outlining the role of the village and its neighbours in the Reconquest.

The tower and ramparts of Olvera castle were restored by the Christians, but they usually preferred to erect their own buildings.

Mosques were pulled down, and churches built in their place, often out of proportion to the smallness of the village, and as dominant on the horizon as the fortresses that preceded them. In Jimena de la Frontera, a Franciscan convent was founded, and the red-brick church of Santa Maria La Coronada is a prominent landmark. The Moorish fortress has long been abandoned, although it still has its tower, as well as an ancient Moorish gateway and the remains of 13th-century Muslim cisterns. Once the site of heavy fighting, the only evidence of any life there now is the braying of a donkey and the tinkling bell of a goat which has strayed to the top of the peak.

The names of several of the pueblos blancos have the words 'de la frontera' attached: Jimena, Castellar, Arcos, Cortes, Vejer. These were frontier villages, but the frontier changed as battles were won and lost, the Muslims struggling to hold on to their terrain, the Christians desperate to win it back. This was hostile country, with the villages spreading across the mountains of four rugged sierras, those of Grazalema, Margarita, Ronda and Ubrique.

The landscape is particularly striking in the village of Grazalema itself, a charming little place surrounded by stark peaks of grey rock.

Its centre could be the template for almost any Spanish village. The oblong expanse of the main square, the Plaza de Espana, is surrounded by trees. At one end is the church of the Aurora, almost the only thing not painted white, and opposite is the casa consistorial, or town hall. In the middle, one of the local cafes has put out some tables, in case anyone should want to eat in the blazing sun. Bizarrely, despite the intense heat of the sierra, the influence of the Atlantic means Grazalema is the wettest place in Spain.

The pueblos blancos are bunched together between the towns of Arcos, to the west, and Ronda, further east. For reasons that appear to have more to do with tourism than anything else, several routes have been mapped out to help visitors find their way around. Most dramatic is the one that goes through the centre, through the winding roads of the Sierra de Grazalema, and taking in Zahara, El Bosque, Ubrique and Grazalema itself. The western route, from Arcos, through Bornos, Villamartin and Algodonales to Olvera, is gentler.

There is also a single-track railway, part of the dramatic route that links Algeciras with Ronda. It was built in 1892 by a British engineer, and was intended originally to take expatriates from Gibraltar up to Ronda. Although the steam engines that once operated have now been abandoned, there are still five trains a day in each direction, stopping at the villages of Jimena, Gaucin and Benaojan (near the idyllic mountain village of Montejaque) and continuing on up to Bobadilla. And you can still stay where the first tourists stayed, at the Hotel Reina Victoria. Built to coincide with the opening of the railway, the 'Queen Victoria' stands out among the other buildings of Ronda, its Northern-European sloping roofs and chimneys a striking contrast with everything else around. Another good option is the parador hotel, a modern building located on the edge of the town's famous gorge.

Despite the existence of public transport and the mapping out of easy itineraries, the white villages have not exactly been flooded with tourists. Visitors flock to Arcos and Ronda, larger and livelier than the villages in between, and more easily accessible. It is a pity to ignore the pueblos blancos, though. Smaller, quieter and less obviously enthusiastic about visitors, their steep alleys, unexpected squares and ancient buildings are full of the essential charm of this frontier region.

FACTFILE

>> All of the major tour operators operate to Andalucia. If you book a package holiday in, say, Marbella or Fuengirola, you're a couple of hours from the delights of Ronda. Check out www. holidaysonline. ie

>> Travelling independently you can fly into Malaga (Aer Lingus, Cityjet, Ryanair or flightonly on a charter) or into Seville (with Aer Lingus), both of which are fascinating cities in themselves and also good starting points for the interior towns and villages of the region.

>> You'll see the area at its best if you hire a car . . . check out Sky Cars, www. skycars. ie . . .for competitive rates and an efficient service.

>> Spanish Railways: 00 34 902 240 202; www. renfe. es