How did Renaissance architects use ancient Roman ruins and Vitruvius's writings?

During the Renaissance, architects sought to revive Classical antiquity by deriving knowledge from two primary sources: the physical ruins of ancient buildings and the treatise De architectura by the Roman architect Vitruvius.12

Use of Ancient Ruins

Architects studied surviving structures, such as the Colosseum and the Theatre of Marcellus, to understand Roman construction techniques and aesthetics. From these ruins, they adopted:1
* The Orders: They utilized the five architectural orders—Tuscan, Doric, Ionic, Corinthian, and Composite—often superimposing them on building stories to create logical, hierarchical relationships.1
* Structural Elements: They incorporated the round arch, tunnel vault, and dome into their designs.12

Influence of Vitruvius

Vitruvius’s writings provided the theoretical framework for Renaissance design. Architects were particularly influenced by his emphasis on proportion as the foundation of beauty. Following Vitruvian principles, they sought a "reasoned harmony" between the proportions of the human body and those of their buildings. This focus on mathematical harmony and clear, measured space distinguished Renaissance architecture from the complex Gothic style. Vitruvius’s work also inspired a flourishing of architectural theory, leading figures like Leon Battista Alberti to publish influential treatises that codified these Classical ideals for future generations.12