Ancient Roman architecture
Although concrete had been used on a minor scale in Mesopotamia, Roman architects perfected Roman concrete and used it in buildings where it could stand on its own and support a great deal of weight. The first use of concrete by the Romans was in the town of Cosa sometime after 273 BC. Ancient Roman concrete was a mixture of lime mortar, aggregate, pozzolana, water, and stones, and was stronger than previously-used concretes. The ancient builders placed these ingredients in wooden frames where they hardened and bonded to a facing of stones or (more frequently) bricks. The aggregates used were often much larger than in modern concrete, amounting to rubble.
Concrete ship
Concrete ships are built of steel and ferrocement (reinforced concrete) instead of more traditional materials, such as steel or wood. The advantage of ferrocement construction is that materials are cheap and readily available, while the disadvantages are that construction labor costs are high, as are operating costs. (Ferrocement ships require thick hulls, resulting in a comparatively large cross-sectional area to push through the water, or less space for cargo.) During the late 19th century, there were concrete river barges in Europe, and during both World War I and World War II, steel shortages led the US military to order the construction of small fleets of ocean-going concrete ships, the largest of which was the SS "Selma". Few concrete ships were completed in time to see wartime service during World War I, but during 1944 and 1945, concrete ships and barges were used to support U.S. and British invasions in Europe and the Pacific. Since the late 1930s, there have also been ferrocement pleasure boats.