A ramp with a length of more than one meter, each staircase, with more than three stages, each landing, balcony, balcony, terrace, outside the corridor

The function of a ladder-only - help us to overcome the space vertically from level to level.

The man, in fact, began its evolution is not to stick-digger: just think he was not in the plane and in three-dimensional space, and the first invention