from his string of remounts. They could survive a whole month on only drinking mare's milk combined with mare's blood. Heavier equipment was brought up by well organized supply trains. Wagons and carts carried, amongst other things, large stockpiles of arrows. The main logistical factor limiting their advance was finding enough food and water for their animals. This would lead to serious difficulties during some of the Mongol campaigns, such as their conflicts with the Mamluks, the arid terrain of Syria and the Levant making it difficult for large Mongol armies to penetrate the region, especially given the Mamluks' scorched earth policy of burning grazing lands throughout the region. It also limited the Mongol ability to exploit their success following the Battle of Mohi, as even the Great Hungarian Plain was not large enough to provide grazing for all the flocks and herds following Subutai's army permanently. Communications The Mongols established a system of postal-relay horse stations called Örtöö, for the fast transfer of written messages. The Mongol mail system was the first such empire-wide service since the Roman Empire. Additionally, Mongol battlefield communication utilized signal flags and horns and to a lesser extent, signal arrows to communicate movement orders during combat. Armor The basic armor of the Mongol fighting man consisted of a heavy coat fastened at the waist by a leather belt. From the belt would hang his sword, dagger, and possibly an axe. This long robe-like coat would double over, left breast over right, and be secured with a button a few inches below the right armpit. The coat was lined with fur. Underneath the coat, a shirt-like undergarment with long, wide sleeves was commonly worn. Silk and metallic thread were increasingly used. The Mongols wore protective heavy silk undershirts. Even if an arrow pierced their mail or leather outer garment, the silk from the undershirt would stretch to wrap itself around the arrow as it entered the body, reducing damage caused by the arrow shaft, and making removal of the arrow easier. The boots were made from felt and leather and, though heavy, would be comfortable and wide enough to accommodate the trousers tucked in before being laced tightly. They were heelless, though the soles were thick and lined with fur. Worn with felt socks, the feet were unlikely to get cold. Lamellar armor was worn over the thick coat. The armor was composed of small