A monument assembly refers to a permanent control point typically placed for future surveying and layout referencing on a road. A monument is typically originally placed for horizontal survey referencing but after placed may be later used for vertical reference as well. The monument is typically placed in the ground or pavement towards the completion of a project, when final grades are achieved and aren’t expected to move,  and is commonly constructed of a concrete foundation with a steel, aluminum, or bronze pin, bolt, or cap cast or epoxied onto the surface.

The monument may be cored into pavement, left exposed, or placed within a cast iron ‘box’ with a lid.  A monument’s concrete structure is laid out with 4 ‘short reference points’ off of which perpendicular strings are pulled to create the precise center of the structure. Then those reference points are used again to place the pin, bolt, or cap. Once the pin or disc is in its final position, a licensed surveyor or the owner of the project will place a final marker or score a permanent mark in the metal to signify the exact final reference point within hundreds of an inch tolerance.