Su Song leads between 1086 and 1092 the construction of a hydromechanical clock tower about 10 meters tall in Kaifeng, the Song capital, documented in the treatise Xinyi Xiangfayao (1092). The mechanism incorporates the first known mechanical escapement operating continuously and the first power-transmission chain (tian ti, 'celestial ladder') documented in history. The tower housed a mechanically driven armillary sphere synchronized with the actual motion of the stars, a celestial globe, and 133 automatic figures to signal hours and quarters. It was dismantled by the Jurchen army in 1127 when they took Kaifeng and transported north, where it was never reassembled. Knowledge of the escapement reached Europe c. 1300; a direct link is debated but chronologically possible.