The Pantheon here was built by the Emperor Haydrian in the 2nd century AD and its 1)dome is still one of the largest 2)concrete domes in the world. It's 50 yards across and its concrete is up to 20 feet thick.
The word "concrete" comes from the Latin "concretus", meaning grown together or harden. Romanconcrete was a mixture of sand, powdered 3)limestone and stone 4)rubble, pretty well what it is today. To construct 5)arches and 6)vaults, the Romans also developed a lightening. And the higher they went the lighter they made the concrete. In this way they could roof over much larger areas than would be possible with stone.
But one of the problems with concrete is that even after it's hardened, it still absorbs water. So the Romans added a mix of 7)volcanic 8)cinders and clay called "Potsularna". Potsularna reacts with the 9)lime in the 10)mortar and sets quickly. And most important of all, it's resistant to water.
The Romans had invented damp proof concrete, and they used it for the foundations of buildings like the pantheon, for lining reservoirs and for constructing harbors. Concrete allowed the Romans to build big and fast, and thus 11)impose their authority on tribes still living in simple structures of wood or mud. Concrete may well have been one of the secret weapons of the Roman Empire.
1) dome n. 圆屋顶 2) concrete n. 混凝土 3) limestone n. 石灰石 4) rubble n. 碎石 5) arch n. 拱门 6) vault n. 拱顶 7) volcanic a. 火山的 8) cinder n. 灰 9) lime n. 石灰 10) mortar n. 灰泥 11) impose v. 加强