Vitruvius was a Roman engineer who lived about 2,000 years ago. He is best known for writing a book called De Architectura, which is one of the earliest known books about architecture and building techniques. In it, he discusses how to make sure buildings are strong, stable, and good-looking. He also talks about art, city planning, and engineering. Vitruvius's ideas have had a big impact on architecture and design around the world ever since. The most famous part of his book is what he called the "Vitruvian Man," which was a drawing of a man with his arms and legs outstretched within a perfect circle and a square. This image has been used to illustrate proportions, balance, and beauty ever since.