Flame On!

Shouldn't we have shields?

Incendiaries were a thing, and they took a lot of different forms, but fire arrows were not as much as TV/Hollywood and Kevin Costner’s Robin Hood: Prince of Thieves would like us to think.  Sun Tzu has an entire chapter (chapter 12 to be exact) devoted to attacking with fire in The Art of War, but very little of it talks about fire arrows, and none of it to fire arrows in open battle.  You might use fire arrows during a siege or in a similar engagement to torch buildings or tents and whatnot (as Sun Tzu and others discuss). You most likely wouldn't use them on the battlefield. Most likely. There are instances, but they are more exceptions which prove the rule. For example, a flaming arrow might be used by a couple of specific archers as a kind of tracer round, to allow the other archers to adjust their aim, or it might be used as a means of communication.

Some ballistae are bigger than others!

Remember, the greatest advantage of archers is putting enough projectiles into the air at a constant rate so that it becomes difficult to breathe. Adding a combustible, able to withstand being snuffed by the wind, would limit the range and accuracy. It would also limit the rate of fire, and penetration/killing ability of the arrow. You also would have some issues setting people or animals on fire in order to kill or maim them, which would essentially be the point of giving up the other advantages. There were better ways of delivering fire into an enemy formation, such as the various ballistae the Romans used, and which were employed throughout the Medieval era until the cannons and mortars took over the job.  Arrows were best used for the job they were designed—killing.

That’s not to say that fire arrows didn’t have a usage.  They certainly had some utilities.  As I mentioned previously, setting fire to buildings, tents or baggage would certainly be useful.  Sun Tzu talks about setting a camp on fire and following that with an immediate attack.  Fire arrows could also be used for psychological means, frightening troops at night.  I’m sure there’s nothing quite like the sight of a few hundred flaming arrows arcing out of the dark at your campsite.  In naval engagements, fire arrows would serve similar uses for setting rigging and dry timber ablaze.  If not a full fire, at least a small enough one that the enemy ship has to devote some time to dealing with the threat.  But it's useful to keep in mind that it would take a bit of doing to actually get the heavy timbers of most ships to catch on fire.  Go ahead and hold a lighter up to a 2x4, even an especially dry one, and see how fast it catches and the fire spreads.  With ample access to water and muscle (hello, sailor!) putting out the smaller flames wouldn’t be too difficult.  A constant barrage of flaming arrows would be necessary to have the desired impact.

There were a number of enterprising bowyers who set about to “solve” the issue of

I hope you're insured!

applying fire to arrows and still making them effective.  The first, easiest way is to make a thicker arrow shaft, with a longer, metal head where pitch or oil-soaked rags could be wrapped around.  We also have arrowheads with a cage, meant to hold burning coals or other incendiaries.  Some arrows were made with a hollow shaft and an open slit to carry the incendiary.  And, of course, there were arrows meant to use or deliver a load of gunpowder, but that goes beyond the scope, and represents a transition time when archery was becoming less prevalent.

Overall, the message to remember here is that flaming arrows did exist, they were totally a thing.  They look damned cool, but that doesn’t make them practical.  But they were a thing with a very specific purpose, and not nearly as common as modern media would like us to believe.