How slowly one travelled in olden days (2,6)

I believe the answer is:

by stages

I'm a little stuck... Click here to teach me more about this clue!

If this is the answer I cannot explain how the clue works.

(Other definitions for by stages that I've seen before include "as Christmas guests might once have travelled" , "Steadily" .)

I've seen this clue in The Globe and Mail.

Want a hint initially instead of a full solution? Install my app