I am interested in ancient technology. Today, we often forget how ingenious ancient people actually were at times. Huge projects were done with very little in way of tools.
Such a military application was Greek fire. Ive read there are not actual surviving formulas for it, but it was an incredible ancient weapon.
It is interesting. When you see images of how the Coliseum looked when it was built, or the Pyramids, which reach back either further in time, it is remarkable what people could achieve with hand tools.
The Pantheon, which replaced in concrete what had been a mostly wood structure built by Marcus Agrippa (burned in the Nero fire; the current structure is still Roman in date, and the original dedication was put on it), remains a marvel of construction, and figuring out how they’d done it only happened in the past few years. And there are the aqueducts, some of which continued to run for centuries without preventive maintenance. And a water-carrying tunnel system (over 70 miles long) in the Holy Land. And their system of roads...
Their artillery (which on the low end includes slings and javelins, but also includes catapaults of various kinds) enabled the Romans to reduce the Gaulic oppida hillforts, and during an early phase of the conquest of Britain, the British hillforts. Vespasian specialized in it, and served in Britain and Judea before he became Emperor. It was shock and awe in the ancient world.