Civil engineering has existed since ancient times when humans first began constructing shelters and buildings. Some of the earliest large constructions were pyramids and temples built by ancient Egyptians and Mesopotamians as early as 4000 BC. Civilization advanced with improved construction techniques by Romans and others who built aqueducts, roads, and other infrastructure throughout their empires. Today, civil engineers design and build structures and systems that are essential to modern life such as roads, bridges, dams, irrigation works, water and waste systems, and more, improving public health and quality of life.