*landmark*

n. [ AS. landmearc. See Land, and Mark a sign. ] 1. A mark to designate the boundary of land; any mark or fixed object (as a marked tree, a stone, a ditch, or a heap of stones) by which the limits of a farm, a town, or other portion of territory may be known and preserved. [ 1913 Webster ]

2. Any conspicuous object on land that serves as a guide; some prominent object, as a hill or steeple. [ 1913 Webster ]

3. A structure that has special significance, such as a building with historical associations; especially, a building that is protected from destruction or alteration by special laws intended to preserve structures of historical significance; as, a landmark preservation law. [ PJC ]

4. An event or accomplishment of great significance; as, Brown v. Board of Education was a landmark of the civil rights movement. Also used attributively, as a landmark court decision. [ PJC ]

Landmarks of history, important events by which eras or conditions are determined. [ 1913 Webster ]