Art and music often share the same characteristics and movements. During a classical period, the emphasis is on perfection and balance. Think of a circle: perfect, contained and complete. The problem with any classical movement, however, is that it is incredibly difficult to maintain. The strain of holding together a classical music piece or creating a perfect sculpture will eventually become too much for the artist.
This is why the movement that follows a classical period is more romantic and fluid, like Baroque. Things no longer have to fit together perfectly. The Baroque period is more like a spiral. There is always a pull towards excess, and the longer the period last, the more ornate and excessive things become. This spiral downward eventually collapsed under its own weight during the Rococo period. If one choir was good, three would be better. If one angel was good in a painting, a hundred would be better.