When the Persian danger was removed, Athens gradually emerged as a leading power in Greece, beginning a period of economic and social prosperity, as well as period of political change. The democratic state was consolidated with new legal reforms. A cycle of intense building activity began throughout the city.
The projects reached their peak when Pericles became ruler of Athens and initiated a grandiose building program. New, magnificent temples and altars were built on the Acropolis along with a strong surrounding wall. In the surrounding area, old sanctuaries were repaired, and the city began construction of new buildings that served religious, administrative, and artistic purposes.
However, this relatively unclouded period did not last long. Disputes with other cities lead to the outbreak of the Second Peloponnesian War in 431 BCE and the Spartan invasion of Attica the following year. At the same time, the Great Plague of Athens left the city weakened and disorganized. Consequently, a military campaign to Sicily (415-413 BCE) was met with a devastating defeat and Athens became a powder keg of intense political conflicts that resulted in the imposition of an oligarchic regime. When the Peloponnesian War ended in 404 BCE with the military defeat of Athens, it also spelled the end of a period of flourishing that had lasted about fifty years.
In 403 BCE, democracy was restored, but prosperity did not return until the middle of the 4th century. The Athenians began once again to develop new buildings, but the ever-increasing power of the Macedonians and the subsequent defeat of the Athenian and Theban armies by Philip II at the Battle of Chaeronea in 338 BCE forced them to focus their efforts on defense.