Landmark

wiktionary

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From Middle English *landmark, from Old English landmearc(“boundary”), from Proto-West Germanic *landamarku(“boundary, landmark”). Equivalent to land +‎ mark. Cognate with German Landmarke(“landmark”), Danish landemærke(“landmark”), Swedish landmärke(“landmark”), Norwegian landemerke(“landmark”) and Faroese landamark(“land frontier”). Compare also Middle English londes-mark(“boundary”).

etymonline

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landmark (n.)

Old English landmearc "object set up to mark the boundaries of a kingdom, estate, etc.," from land (n.) + mearc in its sense "object which marks a boundary or limit" (see mark (n.1)). General sense of "conspicuous object which, by its known position, serves as a guide to a traveler," originally especially an object that can be seen from sea, is from 1560s. Modern figurative sense of "event, etc., considered a high point in history" is from 1859.