How did the ancient Greeks measure the height of the pyramids?

How high are the pyramids in ancient Egypt?

According to historical records, Thales, a Greek mathematician and astronomer, used similar triangles's principle to measure the height of the pyramids. His method is to erect a pole in the shadow at the top of the pyramid and form two similar triangles with the help of sunlight. The ratio of the height of the tower to the height of the pole is equal to the ratio of the shadow length of the two. From this, the height of the pyramid can be calculated.