His wisdom reached many territories, going all the way to Egypt. So the Egyptians then invited him to measure the height of their pyramids, a great feat for the current period, as there was no type of equipment that could easily do so. Thales was able to measure the height of the pyramid using what we know today as the Thales Theorem. In order to devise this theorem he used the shadow caused by the sun and because of this process his reputation as a great mathematician and thinker, became even greater. (source: http://www.estudopratico.com.br/teorema-de-tales/)