This tower is a cylinder. Each level of bricks can be considered as a separate cylinder. If you look thouroughly at that picture you may notice that each level of bricks has different shape. Especially, if you compare the bottom and the top levels. Why does it happen?

Because there is a perspective. For perspective one of the most important things is an eye level. On an eye level everything becomes just a straight line. You can see that - white line is an eye level. Along this line a curve for the border of a cylinder became a straight line.

All brick levels under the eye level have oval shapes.

The same thing for the levels above the eye level.

The farther we go from the eye level the bigger a diameter of an oval.

Another example of how that works - Tower of Pisa

Here as well

This picture illustrastes the perspective rules for cylinders in more precise way.