How did Solon replace government based only on noble birth?

Solon replaced the government monopoly held by the eupatridae (the aristocracy of birth) by instituting a new political constitution based on wealth rather than lineage.12

To achieve this, he implemented the following measures:

• Census of Wealth: Solon established a census that categorized citizens into four income groups based on their annual agricultural production—specifically grain, oil, and wine. Those with income in other forms were rated using a system of equivalents.1
• Redistribution of Privilege: Political rights and responsibilities were allotted according to these income divisions, effectively removing birth as a requirement for holding office. While higher governmental posts remained reserved for the top two income groups, the system opened participation to wealthy citizens who were previously excluded.13
• Empowerment of the Assembly: All citizens were granted the right to attend the general Assembly (Ecclesia), which became the sovereign body responsible for passing laws, electing officials, and hearing appeals from court decisions.1
• Council of Four Hundred: He created a new Council of Four Hundred to prepare business for the Assembly, open to all citizens except those in the poorest income group.1

These reforms laid the foundations for future democracy by shifting the basis of political power from hereditary status to economic standing.1