The below pictures and instructions
will provide a clue of how these Megaliths were built. This is of
course, the Elliptical Plan. Remember that Professor
Thom found that he could use the Megalithical
Yard to construct these plans.

We begin with a triangle. We can construct this triangle by using the megalithical yard to measure its sides. Professor Thom found that in most elliptical plans, these triangles were pythagorean. Hence, this is a pythagorean right angled triangle.

We then name its vertices with the names shown. F-1 refers to 'focus 1'. This information is useful, since we know that ellipses have two foci. Note the the hypotenuse is equal to the side OA.

After constructing the previous triangle, we can construct another just like it, beside it. Or in other words, we can mirror the previous image, so that the full picture now looks like the one shown above.

After we obtain the picture previously, we can mirror that image again along the horizontal line, to get the picture above.

Afterward, we draw the arc, as shown above to obtain an elliptical plan.
This is one of the ways of constructing an ellipse.