《北史·本记·卷九》
黄河长达万里，防御困难，只要有一处渡过，就大势已去。 
且长河万里，捍御为难，一处得度，大事去矣。 
The Yellow River is thousands of miles long, and it is difficult to defend. As long as one place crosses the river, the general situation will be over.