Each May, from morning to night, for as many as five consecutive days, Javier Castillo dances. Coaxed by the rhythms of goatskin drums and wooden rattles, he silently kicks up orange dust on a shimmering lot beside the Rio Grande. God watches.

Rigorous and solemn, these days of dance preserve a folk ritual created centuries ago in a few southwest Texas villages. It is a path to Castillo's past, and an expression of his religious faith.

"This is a very old tradition. I must do all I can to keep it going," Castillo says quietly in a Spanish accent punctuated with humble grins. He is 24, and first participated in the ceremony when he was 5. "I will be dancing until I'm too old to dance anymore. One day I will tell my children they must do the same."

Castillo dances with the 60 or so members of Los Matachines de la Ladrillera -- devout lay persons from a small working-class neighborhood in Laredo, Tex. Seventeen of them are here to demonstrate their rite each afternoon as part of the Smithsonian's Festival of American Folklife, which ends tomorrow.

"The dance is an example of how a revered heritage can tie generations together," said Norma Cantu, a Laredo resident who has researched the ritual and is presenting it at the festival. "The community is really bound by this. It's something that is always looked forward to all year, and can last for six days, almost nonstop except for sleep, even with the temperature usually near 100 degrees."

Initially the dancers were hesitant to travel to Washington, worried that they would be perceived as a performance troupe, not as individuals fulfilling a sacred obligation -- to venerate the legend of Santa Cruz, the Holy Cross.

That legend, as best Cantu can determine it, goes like this: St. Helena discovered the cross upon which Christ was crucified. She gave it to her son, Emperor Constantine of Rome, who soon converted to Christianity. Somehow -- Cantu shrugs as she continues -- the cross is believed to have reached a woman named Malinche, a Native American and companion of the Spanish explorer Hernando Corte's, who discovered Mexico in 1519. Some of the European settlers who followed Corte's to Mexico and what is now the southwestern United States learned the legend, began celebrating the Holy Cross and passed the ritual down to their children, and their children's children, and so on.

The presentation of the dance lasts a few hours each day. It begins with one of the participants carrying a seven-foot cross draped with flowers to a sandy path on the Mall. The dancers circle the cross, shuffle toward it, then drift away in a complex pattern of energetic footwork. Everyone wears hand-crafted red velvet skirts strung meticulously with gold bells, tiny beads of all colors and polished bamboo reeds chopped from the banks of the Rio Grande. Drums beat. Rattles shake. No one speaks.

"It looks real serious, and it is," Castillo says. He pauses and smiles. "But everyone is also very happy, very excited to be getting closer to God."

The members of Los Matachines are very old, very young and very proud. A few feet from Castillo, an elder among the group delicately stitches beads onto a skirt and chats with festival visitors. "Yes, I still dance. I always have," he says. "It doesn't matter that I'm this old. This year I danced for, I bet, 35 hours. And I never, ever got tired."

The tradition is both religious vow and cultural reflex. Some struggle to find words to express its meaning. "I think we're showing our conviction, our heritage," Castillo says. "And I know I must also dance for my brother. I promised."

Castillo's brother Felix died of heart disease 12 years ago. He was 15. It was Felix who introduced his younger brother to the dance, sprinting with him each spring down to the river to gather armfuls of bamboo, helping him make costumes.

"We used to practice together all the time," Castillo says softly. "I remember we'd come home from school, and do our homework quick, then practice. Sometimes I know we even skipped supper. And sometimes me and my brother would be in the kitchen real late, still practicing. And my mother would say, 'Shut up in there. It's 12 o'clock. Go to bed.' And we'd say back, 'But Mom, we're doing the dance.' And she would leave us alone.

"So when my brother died, he told me right before just to keep going every year, to never miss the dance."