Read the paragraph about road building in the ancient Roman Empire.
(1) The ancient Roman Empire included most of Europe and parts of Asia. (2) The Romans wanted to connect their many cities and seaports. (3) The Romans built a system of roads. (4) The Romans used a mix of clay, chalk, and gravel, which made a form of cement, for the foundation of the road. (5) They put large, flat stones on top of the cement foundation. (6) Some of these roads still exist today.
Which revision that combines sentences 2 and 3 into one sentence most improves their meaning?