Create a BC Era device, weapon (in cad), or marvel as a model or in CAD as a measure of your performance through the year and design skill. 

I designed a trebuchet because it is cool. I used Fusion 360, my choice of CAD software to build it and render it. While it looks a little cartoony on the background, in my honest opinion it still looks awesome and was built to a decent scale.

The trebuchet was a weapon used by large civilizations around the time period the book we are reading (Medea) in Language Arts is placed. While it is not mentioned in the book or really as a part of Greek culture it was in use by other cultures around Asia and the Middle East. Today we dont use trebuchets in active combat but the concept of throwing something really heavy a distance is still used in weapons like the Mortar and just about everyone knows about a trebuchet as an example of an engineering marvel of the period.