The francisca is a throwing-axe used, as the name suggests, by the Franks. The head is a distinctive shape, which makes it distinguishable from a battle-axe. Although I had heard many times of this weapon, I had never felt that I understood it. The problem was this: why would anyone use one instead of a javelin? If it was a battle axe which could also be thrown then this might be an explanation, but if it was a throwing weapon only, then the advantages of javelins recommended themselves so strongly that it was difficult to believe that a people such as the Franks could adopt such an apparently ineffective weapon, even if they had some tribal pride in it.
Javelins are lighter and easier to carry than franciscas. A man might carry a bundle of javelins, whereas he is unlikely to carry more than one francisca. Javelins can be thrown from horseback, can be thrown quickly, can be thrown well even with no run-up, have decent range, good accuracy, good penetration and will always land point-first. By contrast, a francisca can't be thrown very quickly, gains a lot from a run-up, and spins around in flight, making the whole process rather approximate, and will seldom hit the target point-first.
My view of the francisca changed rapidly when I went on a dark-age re-enactment weekend in the Lake District. A few of us had made franciscas, and were trying them out for the first time. The first thing we learned is that the head is so heavy (being chunkier than a battle-axe) that the thing is pretty useless in melee - it is just too unwieldy. The next was to confirm near enough everything I said in the last paragraph. The big revelation came when we started throwing them into an empty space of ground. Franciscas bounce.
If a javelin is parried with a shield, and does not come through, the danger to the target is over. Similarly, if a javelin is seen in flight, it can easily be side-stepped by anyone with enough room to do so, and it will hit the ground and stop. Not so, the francisca. When a francisca hits the ground, it bounces randomly like a rugby ball. The heavy head and long curving haft combine to make this weapon hurl about unpredictably for a few seconds, sometimes leaping over a man's height into the air. If ever one did hit a shield point-first, then it might behave as a javelin, but a more likely strike would bounce off the shield alarmingly. The weight of the whole weapon would ensure that it made a frightening noise against the shield first.
Imagine, then, a large group of Franks attacking a formed-up group of foes. If they all threw at once, shortly before contact, then charged in with swords, then they might well find themselves charging into a formation which has be broken up by many whirling unbalanced sharp implements. Few of the enemy would be badly injured by the volley, but whereas a disciplined soldier could well stand in firm formation against a volley of javelins, I strongly suspect that it would take much more nerve to stand steady with half a dozen bouncing franciscas crashing into him and his neighbours.
Our experiments then showed us that the francisca might well be a very effective weapon, to be used a bit like the pilum: thrown as a volley at fairly close range, during a charge against formed-up foes. Whereas the pilum is a weapon which specialises in depriving the enemy of the full use of his shield, the francisca seems better at depriving him of his formation, which would suit a troop type which hopes to charge straight into the enemy formation, and hack it up from inside, such as a barbarian warband. Warbands, one imagines, also used ferocity and terror as a weapon to put their opponents to flight, and franciscas seem well suited to this.