Desert worship. Cool sanctuary in the ancient, earthen mosques of Mali. In this drought-ridden country, there is not the usual ablution fountain at each mosque's entryway. Here, visitors wash with sand.

Sun penetrates the sand streets and mud buildings of ancient cities situated at the southern edge of the Sahara - so much so that places like Timbuktu, Gao, Mopti, and Djenne feel like open-air ovens. It is said that a person loses three liters of body water an hour just walking in this region. In such ponderous heat, stepping into the cool corridors of a mosque is as much physical relief as spiritual sanctuary. In Mali, most mosques are made of mud brick, and are as ubiquitous and varied as the termite mounds that dot the austere territory. Formed from the earth on which they stand, they seem integral to the landscape, like sand castles on a beach. They have a beauty not of color, but of silhouette, line, and texture. Countless storms of sand or rain have weathered their crenelated walls and conical towers. Their sloping minarets are studded with palmyra sticks, used to scale the buildings to make repairs. Over the years, the mud walls, like the faith of the Mus-lims themselves, have been rebuilt time and time again.

By the 8th century, Muslim-Arab traders from North Africa had begun crossing the seething Sahara, leading huge caravans of camels southward to this region. They carried salt in and gold out, gradually turning cities such as Timbuktu into thriving emporiums. In addition to trade goods, they brought the religious, political, and social culture of Islam - including mosques.

The oldest standing mosque in Mali is Djinguereyby in Timbuktu, built by Kankan Musa, 14th-century emperor of Mali. In the year 1325, Musa made a fabulous pilgrimage to the holy Islamic city of Mecca. En route he arrived in Egypt with 60,000 men, 80 camels laden with 300 pounds of gold apiece, and 500 slaves, each carrying a four-pound bar of gold. In Cairo, the value of the local currency, which was tied to gold, was depressed for some 12 years because of Musa's lavish gift-giving.

Egypt had at least as much impact on Musa as the royal pilgrim did on it. It was here that he met the famous Muslim architect As-Sahili and persuaded him to come to Mali and oversee the building of the Djinguereyby mosque. Its mud-brick construction became a kind of architectural model for future mosques in the region.

In addition to Djinguereyby, there are two other ancient mosques in Timbuktu. Near the marketplace stands a smaller, 15th-century mosque named Sidi Yahya. Just above road level there is a small shuttered window in this mosque's wall. It overlooks the grave of a marabout (Muslim holy man).

Legend has it that in days of yore, men accused of crimes were brought to this window and forced to thrust their heads through the opening until they could see the grave. If a man was guilty, he died instantly of terror. If innocent, he showed no fear.

Another mosque, the Sankore, became a university in the 15th century, during the reign of Emperor Askia Muhammed. In this era, Timbuktu grew into a consummate cultural and intellectual center, drawing scholars from many corners of Africa. More than 20,000 students attended some 180 Koranic schools in the city, and pound for pound books sold for more than any other trade item, including gold.

A Sudanese proverb of the day claimed, ``Salt comes from the north, gold from the south, and silver from the city of white men. But the word of God and the treasures of wisdom are only to be found in Timbuktu.''

When Askia Muhammed died in the 16th century, a grand mosque was built in his honor in Gao, east of Timbuktu. The emperor is buried in a pyramid in the central courtyard of the mosque, his tomb surrounded by prayer chambers. As in other corners of the world, Muslims must wash their hands and feet before stepping inside. But in this drought-ridden country, there is not the usual ablution fountain at each mosque's entryway. Here, visitors wash with sand.

Perhaps the most renowned mosque in Mali is in Djenne, a city southwest of Timbuktu. This sublime structure has 100 columns, and towers over the city's brilliantly colorful marketplace. From its sun-struck central courtyard, sun filters into the surrounding naves. The deeper in one walks, the darker and cooler it becomes.

Inside these shadowy, arched corridors, netting hangs from the ceiling for birds to nest in. Rolled straw mats and goatskins lean against the walls waiting for the faithful to come and lay them out on the sand floor. The interior is as simple as a desert landscape. Nothing glitters.

Within the divine dullness of these walls, one's thoughts, undistracted, turn inward and deep.