Today, large concrete structures (for example, dams and multi-storey car parks) are usually made with reinforced concrete.After the Roman Empire collapsed, use of concrete became rare until the technology was redeveloped in the mid-18th century.They kept the cisterns secret as these enabled the Nabataea to thrive in the desert.
After the Roman Empire, the use of burned lime and pozzolana was greatly reduced until the technique was all but forgotten between 500 and the 14th century.
The widespread use of concrete in many Roman structures ensured that many survive to the present day.
The Baths of Caracalla in Rome are just one example.
Modern structural concrete differs from Roman concrete in two important details.
First, its mix consistency is fluid and homogeneous, allowing it to be poured into forms rather than requiring hand-layering together with the placement of aggregate, which, in Roman practice, often consisted of rubble.
Today, concrete is the most widely used human-made material (measured by tonnage).