Art history, like the military kind, is written by the victors. Thus Florentine Giorgio Vasari's encyclopedic "Lives of the Artists," published in 1550, is a propagandist's account of his home city's starring role in the artistic and intellectual phenomenon we now call the Renaissance.

Sano di Pietro's "Madonna With Child Jesus" (1450-55), top, and "Madonna and Child" (1644), by Raffaello Vanni
Banca Monte Dei Pschi di Siena photo

Historians bought Vasari's line, and today, Florence takes the Renaissance credit -- but it was nearly not so. Once, Florence had a serious artistic rival: its Tuscan neighbor the city-state of Siena. An exhibition of Sienese art, at the Tokyo Station Gallery until Dec. 6, goes a good way toward explaining why.