Before anything else, you need to find some photo reference. The
worst thing you could do is try to draw such a recognizable
structure without the proper reference material. Even those who
aren't experts will know if you just winged it. The first step
here is to lay down a verticle line in the center of the page.
This is mainly a guide line. Next, draw two upward lines on
either side of the image area. These are the base for the walls
of the Colosseum. From the perspective of someone standing on
the ground looking up, the outer walls are not perfectly
verticle. Rather, they tilt inward and grow narrower toward the
top. The shape overall shape of the Colosseum is that of a
cylinder. Check your reference. What you want to do here is lay
down some curved lines that represent each level of the
structure. On a blueprint, these would be straight, horizontal
lines. In perspective, though, the lines become curved. Think of
it like string wrapped around a paint can. Looking at the
reference material more closely, lay