milestone

A stone milepost (or by extension in other materials), one of a series of numbered markers placed along a road at regular intervals, typically at the side of the road or in a median.

An important event in a person's life or career, in the history of a nation, in the life of some project, etc.

Death is another milestone on their way.

Creating a complete map of the human connectome would therefore be a monumental milestone but not the end of the journey to understanding how our brains work.

To place milestones along (a road, etc.).

To plan out a project as a series of major steps.