From the start, throughout, from end to end, as in I've known he was innocent all along. [c. 1600] Also see all along the line.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
How to use all along in a sentence
In hand-sewing when the thread passes from kettlestitch to kettlestitch in each signature it is sewed all-along.Library Bookbinding | Arthur Low Bailey