along
parallele Bewegung — an etwas entlang
Parallel movement — along something
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Der Zaun läuft den Garten entlang.— The fence runs along the garden.
Post-nominal (after the noun) — Akkusativ: "den Fluss entlang". Pre-nominal (before the noun) — Dativ, and rarer: "entlang dem Fluss" (formal, literary). Akk-postponed is the everyday choice.