Being able to divide a right line into two equal segments is a skill of inestimable value in drawing fortifications on paper. When well performed this construction works as well as a measured rule for taking otherwise unknown distances on right lines. It also serves as one among several steps in some of the more complex constructions.

Given a Right Line AB, bisect the line into two equal segments.

Open the compass to a length equal to the distance between Points A and B. Using Points A and B as centers describe arcs on both sides of Line AB that intersect at Point C and D.

Produce a right line from Point C to Point D.

Line CD will be perpendicular to Line AB. Mark the intersection of Line CD with Line AB as Point E.

Point E bisects Line AB into two equal segments, AE and EB.

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