Constructing parallel lines is one of the most common activities needed to draw the various boundary lines required to adequately represent the junction of a fortification's surfaces and slopes. This probably explains the reason for so many different constructions to accomplish this relatively simple task. Of the various parallel constructions this is probably the least accurate since it relies on exactly determining tangent points on the curving arcs, a procedure that can be difficult since in most cases the width of one's drawing instruments tends to cover a greater area than a single exacting tangent point.

Given a Right Line AB construct a second line parallel to Line AB.

Select any point (C) on Line AB.

Using Point C as center describe an arc of a circle with a radius equal to the desired distance the parallel line will be from Line AB.

Select a second point (D) on Line AB. Using Point D as center describe an arc of a circle equal to the radius of the first described arc on the same side of Line AB as the first arc.

Carefully place a straightedge so that it is aligned with tangent points on the two described arcs at points E and F. Draw a line that passes through those two points (E and F). This line will be parallel to Line AB.

~ An Instructive Animation Wherein the Foregoing Construction is Visually Explained ~