The ancient Greeks and Romans built artificial pools for athletic training in the palaestras, for nautical games and for military exercises. Roman emperors had private swimming pools in which fish were also kept, hence one of the Latin words for a pool, piscina. The first heated swimming pool was built by Gaius Maecenas of Rome in the first century BC. Gaius Maecenas was a rich Roman lord and considered one of the first patrons of arts.
One of the largest swimming pools ever built was reputedly in Moscow after the Palace of Soviets remained uncompleted. The foundations were converted into the Moskva Pool open air swimming pool after the process of de-Stalinisation.
Most pools in the world are measured in metres, but in the United States pools are often measured in feet and yards. In the United Kingdom most pools are in metres, but older pools measured in yards still exist. In the US, pools tend to either be 25 yards (SCY-short course yards), 25 metres (SCM-short course metres) or 50 metres (long course). US high schools and the NCAA conduct short course (25 yards) competition. There also exist many pools 33⅓ m long, so that 3 lengths = 100 m. This pool dimension is commonly used to accommodate water polo.
The depth of a swimming pool depends on the purpose of the pool, and whether it is open to the public or strictly for private use. If it is a private casual, relaxing pool, it may go from 1.0 to 2.0 m (3.3 to 6.6 ft) deep. If it is a public pool designed for diving, it may slope from 3.0 to 5.5 m (9.8 to 18.0 ft) in the deep end. A children's play pool may be from 0.3 to 1.2 m (1 to 4 ft) deep.
Most public pools have differing depths to accommodate different swimmer requirements. In many jurisdictions, it is a requirement to show the water depth with clearly marked depths afresponsive to the pool walls.