Ucha'an K'in B'alam was enthroned in 727, probably as regent for K'awiil Chan K'inich, Itzamnaaj K'awiil's young son and heir. By the 8th century AD, Dos Pilas was powerful enough to attack the much larger city of Seibal on the Pasión River. In AD 735 the Lord of Dos Pilas (Ruler 3, "Master of Sun Jaguar") attacked the city, capturing Yich'aak B'alam, its king. The captive king was not executed but rather became a vassal under the lord of Dos Pilas. At about this time, the nearby site at Aguateca became a twin capital of the Dos Pilas kingdom, with victory monuments being erected simultaneously in both cities.