his father appointed him the commander of 10,000 horsemen. Due to his reputation for bravery, Modu began to gather a group of extremely loyal warriors. He invented a signaling arrow that made a whistling sound in flight and trained his men to shoot in the direction of the sound in synchrony. To be sure of his men's loyalty, Modu commanded the warriors to shoot his favourite horse, any who refused to do so being summarily executed. He later repeated this test of loyalty, but with one of his favourite wives and once again executed those who hesitated to carry out his order. Only when he was convinced of the absolute loyalty of his remaining warriors did he order them to shoot his father during a hunting trip, killing him in a shower of arrows. With none of his followers failing to shoot at his command and the removal of his father, Modu proclaimed himself Chanyu of the Xiongnu. After his self-proclaimed ascension as Chanyu, Modu began to eliminate those who would prove a threat to his newly acquired power. Thus, he proceeded to execute his rival half-brother, his step-mother and other Xiongnu officials who refused to support his rule. Rise of the Xiongnu Empire Modu's Xiongnu Empire aggressively protected and expanded their territory. When their eastern neighbors, the Donghu, expressed desire to occupy uninhabited land that lay between them, Modu reacted by attacking them. By 208 BCE, the Donghu had been defeated and their remnants split into the Xianbei and Wuhuan tribes. Modun went on to subdue the Dingling and other peoples to the north, and defeat the Yuezhi in 203 BCE. After these conquests, all Xiongnu lords submitted to him. With these victories, he was able to gain control of the important trade routes, which later supplied the Xiongnu with a large income. War with Han dynasty In 200 BCE, Xin, King of Han, surrendered to the Xiongnu at Mayi, Shuofang, Dai Commandery, and joined them in raiding Han territory. Emperor Gaozu of Han led an army against them and scattered their forces, defeating them several times before they retreated. Later Xin set up Zhao Li as King of Zhao and marched south against Gaozu. They too were defeated. Seeing the influence the Xiongnu had on his vassals, Gaozu marched north with a 320,000 strong army to confront them. However his men suffered from inadequate clothing to ward off