The ancient civilization that significantly contributed to modern-day democracy through its assembly of citizens is Ancient Greece, particularly the city-state of Athens. In the 5th century BCE, Athens developed a form of direct democracy where eligible citizens participated in decision-making processes. They gathered in the Assembly to discuss and vote on issues, legislation, and policies. This model of civic engagement and political participation influenced later democratic systems, embedding principles like citizenship, civic duty, and collective decision-making into the fabric of modern democratic governance.