In agriculture, a terrace is a piece of sloped plane that has been cut into a series of successively receding flat surfaces or platforms, which resemble steps, for the purposes of more effective farming. This type of landscaping is therefore called terracing. Graduated terrace steps are commonly used to farm on hilly or mountainous terrain. Terraced fields decrease both erosion and surface runoff, and may be used to support growing crops that require irrigation, such as rice. The Rice Terraces of the Philippine Cordilleras have been designated as a UNESCO World Heritage Site because of the significance of this technique. Terraced paddy fields are used widely in rice, wheat and barley farming in east, south, southwest, and southeast Asia, as well as the Mediterranean Basin, Africa, and South America. Drier-climate terrace farming is common throughout the Mediterranean Basin, where they are used for vineyards, olive trees, cork oak, and other crops. The Yemen Highlands are known for their terrace systems which were constructed at the beginning of Bronze Age in the 3rd millennium BC. Terracing is also used for sloping terrain; the Hanging Gardens of Babylon may have been built on an artificial mountain with stepped terraces, such as those on a ziggurat. At the seaside Villa of the Papyri in Herculaneum, the villa gardens of Julius Caesar's father-in-law were designed in terraces to give pleasant and varied views of the Bay of Naples. Intensive terrace farming is believed to have been practiced before the early 15th century AD in West Africa. Terraces were used by many groups, notably the Mafa, Ngas, Gwoza, and the Dogon. It was long held that steep mountain landscapes are not conducive to, or do not even permit, agricultural mechanization. In the 1970s in the European Alps, pasture farms began mechanizing the management of alpine pastures and harvesting of forage grasses through use of single axle two-wheel tractors (2WTs) and very low center of gravity articulated steering 4-wheel tractors.