From en.wiktionary.org:
** German
*** Alternative forms
- [de]
*** Etymology
[de], cognate with [de] (with a gliding sound _-t-_).
*** Pronunciation
- [de]
- [de]
- [de]
- [de]
*** Adverb
[de-adv]
1. along
*** Preposition
[de]
1. along ; [indicates location or movement]
1. [de]
2. [de] [de]
*** Postposition
[de] [de]
1. along ; [indicates movement]
**** Usage notes
- A general tendency is to use the preposition with verbs showing location and the postposition with verbs of motion.
- Postpositional usage is alternatively analyzable as part of a separable verb (such as entlanggehen ).
*** Further reading
- [R:de:DWDS]
- [R:de:UniLeipzig]
- [entlang_seitlich_zuseiten]
- [entlang_laengs_seitwaerts]