7. Pilum
The roman army, at the height of its power, had conquered basically everywhere. The strength of their military was in no small part due to the equipment of the legions. The archetypal Roman soldier was equipped with three things, a gladius, a tower shield and often a pilum or two, the pilum being the focus of this section. A pilum was a javelin with a few simple characteristics that gave some significant tactical advantages. Firstly, the head of the pilum was a pyramid (or tetrahedral shape), so once stuck in something, a ribcage for example, the sharp angle at the base meant it was difficult to pull out and would cause further damage. The really clever part was the shank though, which was relatively thin and often not hardened, therefore prone to bending which meant even if a chap did wrench it out of his fallen mate's ribcage he couldn't then return it to the steadily advancing Romans point first. Even if the pilum stuck in a shield rather than a person it would make the shield unwieldy and take it off balance, making it awkward to handle. In this day and age we often paint a veneer of honour and civility over warfare, but in actual fact never in the history of warfighting has an army paused for an enemy saying "hang on a moment there chaps, I just need to dig this weapon you lobbed at me out of my shield before we really get started". In reality he would receive a sword slamming through his collar bone before he got the third word out. The shank being narrower also meant that once the head had pieced something the shank wouldn't interfere with the edges of the hole, reducing friction, and enabling the tip to drive deeper into the target. Invention doesn't necessarily mean complexity, and this was a great example of simplicity of design making a highly effective weapon.