Name an advance made in Science, Technology, and Mathematics during Hellenistic times?

The Hellenistic Erasistratus discovered the heart was the pump to push blood through the arteries.

Aristarchus developed the theory that the sun was the center of the universe.

Euclid wrote the basic geometry book, Elements, that was used for 2000 years.

Hero of Alexandria devised the first steam engine although he considered it merely a toy.