The carp was a luxury food in the middle and late Roman period, and it was consumed during fasting in the middle Ages. The fish were kept in storage ponds ('piscinae') by the Romans, and later in fish ponds constructed by Christian monasteries. In this European practice the carp were kept in monoculture. The largest individuals were selected as broodfish. From, the 12th to the mid-14th century A.D. unintentional artificial selection had taken place, the first steps towards domestication. Controlled semi-natural pond breeding and fry rearing of carp started in the 19th century in Europe. Cyprinids have been reared in China for more than 2 000 years, where they were kept in undrainable ponds. The ponds were stocked regularly with fry from rivers. Natural food-based polycultural rearing technology was applied. Semi-domesticated carp races have developed in this system. Domesticated carps have been produced in most of the carp rearing areas recently. There are about 30-35 strains of domesticated common carps in Europe. Many strains are maintained in China. There are some Indonesian carp strains, which have not been scientifically examined and identified so far.