The horse collar as the most important high-tech invention.
Developed around 1000 AD in northern Europe, it allowed the region to be farmed efficiently and so, it could be argued, was responsible for the rise of civilization there. It also gave its possessors great war-making potential — think of knights in armour, for example.
Links:
[1] https://www.edge.org/annual-question/what-is-the-most-important-invention-in-the-past-two-thousand-years
[2] https://www.edge.org/inthenews/what-is-the-most-important-invention-in-the-past-two-thousand-years
[3] https://www.edge.org/contributors/what-is-the-most-important-invention-in-the-past-two-thousand-years
[4] https://www.edge.org/responses/what-is-the-most-important-invention-in-the-past-two-thousand-years
[5] https://www.edge.org/memberbio/peter_tallack