Siena's Piazza del Campo is normally a sleepy place, a place for strolling or for lingering at a sidewalk cafe. This wide shell-shaped piazza is a serene place to enjoy thoughts of another time in the eternal Tuscan sunshine.

But on two days each year everything changes. The arched windows of the majestic old palaces fill with spectators, bright banners hanging from every balcony punctuate the everyday soft gray and terra-cotta colors of the city, and the cafe' tables and chairs are taken in to make room for the crowds that jam the piazza for the crazy and colorful horse race known as the Palio.

The Palio is run each year on July 2, in honor of St. Mary of Provenzano,and on Aug. 16, for the Feast of the Assumption. This year the race also will be run on Sept. 13. It is one part solemn pageant and one part madcap scramble around the edge of the Piazza del Campo. But, more than that, it is a link to the city's past that is a part of Siena all year long. No matter when you visit this northern Italian city, you will feel the presence of the Palio.

For all its significance in Sienese life, the Palio itself lasts only minutes, just as long as it takes the 10 competing horses to gallop three times along the dirt track laid for the occasion along the outer edge of the Piazza del Campo. But the brief race is just a part of a year-long cycle of ceremonies and festivals that are woven into the fabric of the city.

The race is a competition among Siena's 17 administrative districts or wards, called Contrade, which are geographic divisions within the walls of the old city that date back perhaps before the devasting year of the Black Death -- 1348. The Contrade are political sectors that elect representatives to the city's government. But to the Sienese, they are much more than that. Each of the Contrade is like an extended family, with its own church, its own museum, its own social club. The events of life within the Contrada are shared by all its residents. Births and marriages are celebrated, deaths are mourned by the entire Contrada community.

*The word "palio" means banner and actually refers to the individual flag that each Contrada defends in the race. The Onde (Wave) Contrada, for example, a recent winner, has on its flag a porpoise riding the crest of a wave. Among the other Contrada symbols are a turtle, a porcupine, a giraffe, a panther, a tower, a forest, a unicorn and a duck, and when Palio fever runs high, they appear on everything from scarves to T-shirts for partisans and souvenir hunters alike.

Few weeks go by in Siena without some festivity, since each Contrada marks the feast day of its patron saint with street fests that often spill over into the surrounding Contrade. Ancient costumes are worn, flags are paraded, and astonishing amounts of food are consumed with enthusiasm.

* Preparations for the Palio itself extend over a period of months, reaching a peak in the three days before the race. Ten Contrade are selected to participate in each Palio, since the course cannot safely accommodate 17 horses. The 10 include the seven Contrade that did not run in the preceding race and an additional three chosen by lot. Each horse is blessed in its Contrada's church, and if the horse misbehaves during the ceremony that is considered an omen of good luck. Trial races are run for the three days preceding the Palio. The excitement builds to the arrival of the race day.

The Palio seems to have lost none of its crowd appeal since July 2, 1656, when it was first run in honor of the Madonna di Provenzano. On Aug. 16, 1701, a second Palio was added to honor the Feast of the Assumption. But the Palio is merely a recent addition to Siena's long history.

Dating back to Etruscan times, the city has preserved its medieval period more completely than any other. During that period, from the end of the 13th to the middle of the 14th century, Siena was one of the greatest of Italian cities -- wealthy, powerful, filled with artists who created lasting treasures. But Siena's prominence was not destined to last. From behind its thick walls the city endured centuries of would-be conquerors, an outbreak of plague and a disastrous siege. It saw its population decimated, its wealth and influence reduced. But along the narrow stone-paved streets, its proud spirit survived. Today Siena's 700-year-old university, its architectural masterpieces and the purity of its dialect that draws language students from throughout the world are reminders of its past.

*It is in part a tribute to the past that brings throngs of Sienese and visitors to the city on Palio day to climb its cobblestone streets like pilgrims up to the Piazza del Campo. They stop to pet the horses waiting to race, and they talk to the riders and pose children with them for photographs. The teen-age boys who will mount the horses have a 17th-century look in their costumes, but that seems only fitting in a city that lives intimately with its past. Strangely, most of the riders are not Sienese, but rather Italians from other areas hired by the Contrade for their skill.Up in the piazza the spectators sweltering in their coolest cottons look with sympathy at the velvet-clad trumpeters. The procession fills the late afternoon as each Contrada parades its colors, its horses and its armored knights slowly around the race course. Standard-bearers put on their flag-throwing shows while drummers mark the procession's steady pace. Although the scooped floor of the piazza makes looking down on the action a little easier, the luckiest viewers are those who are tall and who have a good tolerance for crowds.

Finally it is time for the race. At 7:45 p.m., the bareback horses and their riders enter the square, the signal is given, the crowd gasps, and the gallop begins. For three breakneck laps around the square they race, with not-so-occasional spills, until at last the winning horse, with or without its rider still aboard, crosses the finish line. The triumphant Contrada parades its flag and the post-Palio celebration begins.

The postrace festivities last for days, with outdoor dinners at tables that stretch through the streets of the winning Contrada, welcoming Sienese and visitors alike.

After the racing and the feasting are over the Piazza del Campo becomes its placid self once again. The banners are stored away, and the cafe' tables reappear with their invitation to linger in the sunshine. But listen closely any day of the year and you may hear the faint echo of the galloping hooves of the Palio.