源远流长

源远流长 [yuán yuǎn liú cháng]

1. ■ The source is distant and the stream long.; a distant origin and a long development; a distant source and a long stream -- of long standing and well established; go back to ancient times;（The river of friendship) runs a long course from a remote source:

我们两国人民的友谊源远流长。 The friendship between our two peoples goes back to ancient times.; The river of our friendship runs a long course from a remote source.