It is since Koryo Dynasty that Jeju began to be renowned for an ideal place to raise horses.
It is generally understood that the breeding of horses and cattle came to flourish only after Yuan Dynasty directly ruled Jeju, taking advantage of Jeju for grazing horses and cattles. However, stock farming had been actively carried out earlier, going back to pre-Koryo period. From the early Koryo Dynasty, this line of farming was already prevalent nationwide. Likewise in other islands, Jeju was incorporated and controlled under the administrative unit 'Do' where breeding horses and cattle was the main resource in paying taxes.
As for the configuration of Jeju, gentle slopes stretch from Mt. Halla rising high at the center, down to the coastal areas. The climate of Jeju is rather warmer in winter and cooler in summer compared to that of the mainland. A plenty of grass grows naturally. In addition, rainwater from frequent downpour ran down steeply from high region of Mt. Halla, creating sporadic streams and they acted as a natural fence which horses and cattle could not easily overcome. The area surrounding Mt. Halla gradually elevates as high as 1950m above the sea level, at the peak of the mountain. Along the slope of the mountain, sprouting of grass or leaves progresses upward trend while withering of them advances downward, both of them at a slow pace, that the variation between growing and drooping is clearly seen. With this, the managers of horses and cattle could easily figure out whereabout of their stock.
Admittedly, Jeju is bestowed with the natural ranches for pasturing so as to be believed as a place where the god of stock farming once assumed. Making use of this resource, Jeju residents traditionally used to graze horses and cattle in the wild, which method was not practicable in other regions. This grazing type was closely associated with farming and continued long past Koryo and Chosun Dynasty. Meanwhile, the government's control over the stock in Jeju was exercised by the local powers such as Sungju, Wangja, the equivalents to petty officials in other regions.
Since the late 13th century when the ranch management was under the direct control of Yuan Dynasty officials, the traditional nomadic tribe of Mongol moved in to raise the stock. Between the Mongols and the local residents, the exchange in breeding ways influenced each other, leading to the expansion of stock farming here than before. The knowhow and scale of the stock farming in this period was retained by the local people and Jeju native ponies or Jorangmal began to produce in full scale. As a result, there comes a Korean saying that goes, 'People should be sent to Seoul while horses should be sent to Jeju Island.