According to the regulations of the yasa, the Mongol legal code based on Chinggis Khan's ordinances, the entire empire was the property of the Khan's family, and its members divided up this property according to set principles. Every new conquest necessitated the division of the added spoils. Chinggis's first wife, Börte, bore four male children and Chinggis ‘envisioned each of them as a ruler and called them the four külügs [pillars]', dividing up the empire between them during his lifetime. The youngest son, Tolui, was the ‘guardian of the hearth’ (Mong. otchigin), and thus received the ancient central Mongol regions along the Tola, Onon and Kerulen rivers as his inheritance. The third son, Ögödei, received the territory from Lake Balkhash westwards along the Imil and Irtysh rivers. The second son, Chaghadai (later Chaʾadai), whose name is better known in its Turkic form, Chaghatay, became the official guardian of the yasa, and received the former centre of the Qara Khitai territory along the Ili, Chu and Talas rivers (today's Semirech'e) and later the Transoxania and Kashghar regions also came under his authority Finally, Chinggis awarded the area of the Irtysh River and the Altai Mountains to his first-born son, Jochi, with the command to conquer the western steppe, the Dasht-i Qipchāq, as well.