Line of thrust

The line of thrust is the locus of the points, through which forces pass in a retaining wall or an arch. It is the line, along which internal forces flow,,.

In a stone structure, the line of thrust is a theoretical line that through the structure represents the path of the resultants of the compressive forces,. For a structure to be stable, the line of thrust must lie entirely inside the structure,,.

Where important
The line of thrust is important in almost any architecture bearing weight. This includes aircraft, bridges, plus arches; see catenary arch.

An arch won't collapse, when the line of thrust is entirely internal to the arch,.