Once a rival of Florence, the Black Death ended up bringing about Siena's downfall in power and influence. However, similar to Assisi, this tragedy allowed the medieval part of Siena to be preserved almost like a time capsule.
Now, while it's no longer competitive with Florence in size, it continues to be a favorite place for visitors, and is known for the annual Palio races held in July and August. The 'contrade' (neighborhoods) in Siena are each represented by a horse and rider who are blessed by the churches in their neighborhood. They then race through the packed square of the town while townspeople cheer and wave their respective neighborhood flags. We haven't attended--perhaps we will this year (although we seriously feel like we are running out of time!) We walked down this neighborhood, which had flags proudly displayed along the streets.
In the square (which is really not a square, but amphitheater shaped),
is the Piazza del Campo, is a Palazzo Publico, the public palace, or municipal bulding. There's also the Torre del Mangia, the bell tower, prominently standing next to the Palazzo Publico.
A few streets over is the Duomo. From the outside, the Duomo looked strikingly similar to Florence's giant Duomo, and we could definitely see that the towns had once been very much arch-enemies. We did not go into the Duomo--a long line, an entrance fee, the beginnings of rain and the promise of yet another 3 hours of driving were all major factors in that decision.
Rick Steves suggests that Crayola was inspired by Siena when naming their red-brown clay colored crayon Burnt Sienna.