The Gereg is a traditional Mongolian document that served as a royal decree or passport during the time of the Mongol Empire. It was created by Genghis Khan in the early 13th century to facilitate trade and communication across the vast territories of the empire. The Gereg provided protection and privileges to travelers and merchants, allowing them safe passage through different regions. The document was often made of leather or paper and featured the seal of the khan, signifying its authenticity. The Gereg played a crucial role in establishing the Yam system, which was a network of relay stations that supported the movement of goods and information across the empire.