北京什刹海是永定河历史上留下的许多故道之一。早在商、周时期 ,永定河主流由清河、温榆河方向改道从八宝山以北向东 ,经紫竹院、什刹海 ,沿今坝河方向东流 ;春秋至西汉时又从什刹海向南经今三海、天坛东向东南流注。东汉时又由蓟城北改流蓟城南 ,这次改道后 ,在原故道上留下? Shichahai in Beijing is one of the many historical sites left by the Yongding River. As early as the Shang and Zhou dynasties, the mainstream of the Yongding River was diverted by the Qinghe and Wenyu rivers from north to east of Babaoshan, eastward through the Zizhuyuan and Shichahai along the present dam. From Spring to Autumn, Temple of Heaven East southeast flows. Eastern Han Dynasty by thistle city north of flow thistle south, after the diversion, left in the original road?