Perhaps due to the pleasant tranquillity in Roman times, we have no news of the city of Viterbo for many centuries, until the last of the barbarian invasions, that of the Lombards, who took over territories of Tuscia from the Goths.
Since then, Viterbo grew in and around a fortified hill, to become one of the largest cities of the province. In 1194 the bit key was moved here from Tuscania, and Viterbo began to be contested between the Guelphs loyal to the Pope, guided by the Gatti family, and the Ghibellines faithful to the Emperor, led by the Tignosi family.
Viterbo was finally won by the Guelphs, and became so loyal to the Popes that many of them chose to reside here, after Pope Alexander IV who, among other things, started building the Popes' Palace, Viterbo's most famous monument. Since then, Viterbo is also known as the "City of the Popes".
Piazza Cappella lies in the heart of the San Pellegrino medieval quarter.
More info and virtual tour of Viterbo.