Yassa (alternatively: Yasa, Yasaq, Jazag, Zasag, Mongolian: Их засаг, Yehe Zasag) was a secret written code of law created by Genghis Khan. The word Yassa translates into "order" or "decree". It was the de facto law of the Mongol Empire even though the "law" was kept secret and never made public. The Yassa seem to have its origin as decrees issued in wartime. Later, these decrees were codified and expanded to include cultural and life-style conventions. By keeping the Yassa secret, the decrees could be modified and used selectively. It is believed that the Yassa was supervised by Genghis Khan himself and his stepbrother Shihihutag who was then high judge (in Mongolian: улсын их заргач) of Mongol Empire. Genghis Khan appointed his second son Chagatai (later Chagatai Khan) to oversee the execution of the laws.