Around 600 b.C. the polis of Athens was in deep crisis. The number of free farmers increased rapidly, so they each had less land to get a satisfying yield. Debts and after that slavery were quite suddenly of the order of the day. Politically Athens was in crisis because society changed. Before, the political power through the ecclesia was with the land owners. Now, a seperate economic upper class was formed thanks to trade. This group also wanted political influence.
In 594, the people of Athens gave a man named Solon special powers in legislation to repair the polis' harmony.
Solon abolished slavery by acquitting all debts and forbid future servitude. The principle of a free farmers' society was therefore secured (at least in theory).
His second measure was to rearrange the whole citizenry into four political groups, based on property. Although aristocracy and wealth were still very much parallels in Solon's time, this meant that birth was no longer the criterion for power.
The highest Solon classes were those of pentakosiomedimnoi ('the 500 bushel men') and hippeis (they went to the battlefield by horse, where they subsequently participated in the phalanx as infantry). Only these two classes were available for the highest political functions.
The third class was that of the zeugitai, seemingly welfared farmers who had their own pair of oxen, called zeugos. They could have lower political functions. The fourth and lowest group consisted mainly of day labourers or thetes without their own land or property. They had no military value and therefore could not apply for any political job, but for the first time they did have access to the ecclesia.
To secure a more influencial role for the ecclesia, Solon restricted the power of the Areopagos (high council) and constructed a new council called boulè. This 'Board of 400' assisted the ecclesia by preparing its decisions.