From the beginning of the reign of the dynasty, the Song emperors had to fight off predatory nomads, who on their raids repeatedly penetrated deep into the Chinese Empire. Finally, the Song agreed with the nomads upon the payment of an annual tribute of 200'000 rolls of silk and 100'000 liang silver – one liang equaleing some 1000 cash or about 37 grams (1.3 ounces) of silver. By these payments the Song emperors secured the peace of their realm for a long time.