Yam was a military post, established by Genghis Khan. During the Mongol Empire, such posts were created at a distance of 25 miles. At these posts cavaliers and messengers were appointed and horses were placed at their disposal. These cavaliers used to carry official records from one place to another. Each cavalier was required to tie a bell with the neck of his horse. Whenever, a message used to reach near a post, the messenger present at post, on listening the ring of the bell so tied with the neck of horse, used to get ready along with horse to leave for the next destination. At Yam, proper arrangements were also made for the travellers. With the aim to make their stay secure and comfortable the travellers were issued official passes, known as Paiza. These passes were of three types-gold, silver and iron. The travellers had to tie these passes (Paiza) on their forehead. The travellers were provided facilities at every Yam, according to these passes. The institution proved very successful for the Mongol administration.