Because of the sheer number of sights to see, some first-time visitors like to start out with an organized tour. While few things can really be covered in any depth on these overview tours, they're sometimes useful for getting your bearings.

One of the leading tour operators is American Express, Piazza di Spagna 38 (tel. 06-67641; Metro: Spagna). A popular tour is their 4-hour orientation of Rome and the Vatican, which departs most mornings at 9:30am and costs 60€ ($72) per person. Another 4-hour tour, which focuses on the Rome of antiquity (including visits to the Colosseum, the Roman Forum, the ruins of the Imperial Palace, and San Pietro in Vincoli), costs 60€ ($72). From April to October, a good excursion outside Rome is a 5-hour bus tour to Tivoli, where tours are conducted of the Villa d'Este and its spectacular gardens and the ruins of the Villa Adriana, all for 50€ ($60) per person.

Through Eternity Tours, Via Sinuessa 8 (tel. 06-7009336; mobile 347/336-5298), is staffed by a team of art historians, archaeologists, and experts on ancient Rome. Its guided tour of Vatican City is the best in Rome, a comprehensive 5-hour tour that brings life to the artifacts in this vast treasure trove. The cost is 41€ ($50) per person. Other tours include Rome at Twilight, a 2 1/2-hour evening tour of the city's beautiful piazzas and fountains, costing 27€ ($33) per person; and a 2 1/2-hour tour of the Ancient City costing 27€ ($33) per person.

Another option is Scala Reale, Via Varese 52 (tel. 888/467-1986 in the U.S., or 06-4820911), a cultural association founded by American architect Tom Rankin. He offers small group tours and excursions focusing on the architectural and artistic significance of Rome. Tours include visits to monuments, museums, and piazzas, as well as to neighborhood trattorie. Custom-designed tours are available. Prices begin at 20€ ($24). Children 12 and under are admitted free to walking tours. Tour discounts are available for a group of four.