ETYM Old Eng. along, anlong, AS. andlang, along.
1. In accompaniment or as a companion.
2. In addition (usually followed by 'with').
3. In line with a length or direction (often followed by 'by' or 'beside').
4. To a more advanced state.
5. With a forward motion; SYN. on.

Along the length

1. Across time.
2. With respect to longitude.