The spear may be unique in that it may be the only weapon that every single culture used in warfare. Many nations had their own favourite weapons, some had weapons which only they used, but pretty much everyone came to the same conclusion: that a long pointed stick was an effective weapon of war. Indeed, one sometimes reads of "spears" being used to mean "soldiers".

There isn't a huge amount of functional variation in spears. All spear shafts are straight, and all spearheads are pointed. The shaft of a spear was made of a type of wood which was fairly tough (unlike pine) and which had a grain that ran nicely up and down it, with no lateral faults (unlike oak). A common wood to be used was ash. Handles or grips on spears were pretty rare. They were not necessary, and most men seemed to prefer to be able to slide their hands up and down the shaft freely. Some spears had but the one pointy bit. Many had "butt-spikes" or "ferrules", which were simple cone-shaped additions to the rear end of the spear. These had many uses. They were back-up spearheads in case the main head got blunted or fell off. They made it easy to stick a spear in the ground. They were often favoured for despatching fallen men, especially as a large formation marched over the fallen.

The main functional variation of the spear was its overall length. Many have argued over what length spears were. The evidence is not always conclusive. Many spears come from graves, but the wooden part of the spear has usually rotted away, and the distance between the head and butt-spike is not proof of the spear's length. Perhaps a long spear was broken to fit in the grave. It seems unlikely that someone burying a man with his twelve-foot spear would dig a grave twelve feet long for him. Pictures of spears are not perfectly reliable either. Often spears are shown as short, so that a statue can fit in a pediment, or a relief on a frieze, or a painted figure in a band of design going round a vase.

The shortness of a spear is limited by the advantage that a spear has over other weapons. The thing that makes a spear worth having is that it is quite long. If a spear is as short as a sword, then one should instead be using a sword, since a sword can cut as well as thrust, and is much more strong, wieldy, and versatile in a scrap. To be useful in battle, a spear must be long enough to keep sword and axe and mace-users at bay. Short spears seem to have been about the length of the height of the user. A six-foot man would have a six-foot spear. Again, this seems to accord near enough with the pictorial, written, and archaeological evidence. Persian spears, of the period of the Persian invasion of Greece, seem to have had counterweights on the butt ends of them, rather than butt-spikes.

In the ancient world, armies used shields, and so spears were usually wielded one-handed. The shield is an excellent tool for self-defence, and it was so effective, that almost all cultures used it. Certainly all the armies fighting mass battles in the ancient Mediterranean world had shields. If the enemy is showering you with arrows or sling-stones, you want a shield. A formation of spearmen without shields is very vulnerable

In the vast majority of instances, shield-using spearmen clashed with their foes, using a spear one handed. The spear would have been short enough to wield in that one hand, and could be used to parry enemy weapons, especially if the enemy was using spears. A common clash was between two formations of spearmen.

There are many writers who insist that spears were used over-arm. I believe this to be wrong. The pictorial evidence is very poor. Where spears are shown to be used over-arm, it seems that this is for dramatic effect rather than for authenticity. Archaeology will tell us nothing on this issue, and I have come across no written record from antiquity, which strongly backs up the over-arm theory. I shall now present my case for the under-arm use of spears.
The two competing handholds are as follows:

1. Over-arm: the spear is held in the centre, with the right hand. The hand is held at about head-height, with the elbow of the right arm out to the side. The right thumb of the user is on the head-side of his hand, and his four fingers curl over the top of the spear.

2. Under-arm: the spear is held in the right hand, with the thumb on the top of the spear and the spear held typically at around waist height. The fingers curl under the spear shaft. The spear shaft rests along the underside of the forearm with the butt-spike by the right elbow.

With the over-arm hold, the spear is held in the centre. This means that half the length of the spear is wasted, and serves merely as a counter-weight to the front half. No man would be strong enough to hold a spear horizontally over-arm by one end. This goes dead against the whole idea of a spear. A spear is a device for keeping your enemy at a distance. He cannot come close to hit you with a club or sword, because as he advances to his fighting distance, he gets skewered. An eight-foot spear is turned into a four-foot spear if it is held over-arm. If two formations of spearmen clashed, one using spears underarm, the other over-arm, then the fools using their spears over-arm would face their enemies' spears before they themselves were in striking range.

With the over-arm hold, the rear end of the spear acts as a counterweight to the front end. If a foe were to strike the spearhead sideways with a sword, then the counterweight would act against the spear-user. The front end of the spear would act as a lever, twisting the wrist of the spearman, and the swinging rear counter-weight end would act to exaggerate this effect. To close with a spearman, a sword user has to knock the spearhead aside and rush in at his foe. The over-arm grip would make this much easier. With an under-arm grip, the spearman has his spear braced along his forearm, and has much more control of the spearhead. The spearhead may be knocked aside, but it will resume position a great deal more quickly. If a high thrust over a shield is wanted, this can be achieved by bringing the right elbow up to shoulder height. Also, if the swordsman advances, then the under-arm spear user can retreat a great deal faster, to bring his spearhead between them, as he has the ability denied to the over-arm user, of pulling back his spear, and sliding his right hand up the shaft, to shorten the weapon for close use.

With the under-arm grip, a spearman can thrust with his spear downwards at the feet of his foe, or upward at his face. The strongest thrust he can do is at waist height, and he can disguise his intentions easily. He can hold his shield in position during all of this. Using an over-arm grip, the feet of the foe are out of reach. This suggests that the lower leg was a common target. Not only are the feet out of reach, but the thighs are difficult targets. A thrust at waist height is difficult, and the spear point will be travelling downwards, and will glance of a shield more easily. The only really strong thrust will be at the face and neck of the enemy. The neck was seldom armoured in ancient times. Greeks and Romans usually had no armour there at all. This thrust will be easy to see coming. Worse still, the spearman thrusting over-arm will, of necessity expose himself as he does this, leaning forwards out of formation, and turning his shield to the left to give himself room for the thrust. If an enemy spearman to the right of the over-arm user saw the thrust coming, he would have an easy victim: a man who has stepped with his weight onto his front foot (thus preventing any evasion by footwork) with an exposed shield-less side.

As mentioned above, most ancient spears had butt-spikes, and spears were used in large formations. An under-arm grip allows the butt-spike to be controlled, tucked away where it will do no one any harm. Anyone standing behind an over-arm spearman will be faced with a butt-spike going in and out at every thrust, and unpredictably sideways whenever an enemy knocks the spearhead. If spears were use over-arm, then a lot of people would have had somebody's eye out by mistake.

Spears can be used for parrying, but only if used under-arm. The under-arm spear can be used very effectively to rake the enemy's spears aside. Each man in a formation can act to protect not just himself, but his neighbours this way. Such group strength will win the day against men who cannot act to help their neighbours. Under-arm use of spears also means effectively longer spears, so parries can start further out from the user, which is a big help, and one spear can guard a larger volume of space. The armour that soldiers wore seems to have been designed for under-arm spear use. Hoplite and legionary armour involves stiff broad pieces that cover the shoulders. These make holding an arm up awkward, uncomfortable, weak, and limited. Armpits were generally not armoured. If a man were using a spear over-arm, his right armpit would be exposed all the time during a fight. Many shields had a cut-away in the side that allow a spearman to keep his shield nicely in front of him, and his spear in fighting position - as long as it is underarm. Shields were either round or taller than they were wide. This makes sense if the spear is being used under-arm, since it means that the shield does not get in the way of the spear so much, but is bafflingly daft if the spear is used over-arm, because it would serve simply to further expose the wielder.

A spear used under-arm is easy to set in the ground against a cavalry charge or the like. It is also easy to ditch in favour of a sword when the melee gets frantic and mixed. A spear is easy to deploy underarm. When on the march or standing at rest, a spear would be held vertically, and the spearman simply has to lower the spear into position, and thrust it out in front of him. Greek texts refer to orders given to the men to "lower" spears and advance. To deploy a spear over-arm, a man has to throw the spear upwards, quickly get his arm underneath it, and catch it again (unless he was holding it upside down, with the butt spike in the air, but this is never pictured, and would mean that the main spearhead would get blunted on hard ground).

Another snag with the over-arm grip is that it is very tiring. Just holding your arm up and out to the side can get tiring, without the weight of a spear on it. With the under-arm grip, the spear is held close in to the body, is much easier to hold, and it is much easier to take a rest. During the slightest of lulls in the fray, the spearhead can be lowered to the ground, and from there, it can rapidly be redeployed.

To appreciate the weight of the above arguments, it is necessary to imagine large numbers of spearmen clashing in formation. The front row of each formation would try to present the enemy with spear points, and a wall of shields. From re-enactment experience, I can say with confidence that the person most likely to kill you is not the man opposite you. If you are half-competent with your shield, then you will always be able to move it to block your opponent's thrusts (with the possible exception of thrusts aimed at the feet, and these are only possible with under-arm use). As you fight, you will be watching for an opportunity to make a kill - to thrust through a gap in the enemy's shield-wall. Your enemies are doing the same. When you see a chance to thrust into a gap and take it, then you are for that instant exposed to some extent (utterly exposed if using over-arm). If an enemy has predicted your thrust, then he will spear you as you make it. You defend yourself against the man in front of you, and defend your neighbours from him, while watching for a chance to spear one of his neighbours. With underarm use, his neighbours are in easy reach, and his neighbours' neighbours are in possible reach. With over-arm use, his neighbours are possibly within reach.

Sometimes, the furious charge of one side in a battle would sweep away the enemy. It takes nerve and confidence in one's fellows to stand fast as the enemy rushes on screaming out war cries. Where both sides keep their nerve, however, then two other possibilities arose. One was that both sides would get to spear-using distance, and then halt and fight it out. In such circumstances, under-arm users would have the advantages spelled out above, and more. Spears are sharp. A hard thrust into a shield would cause it to blunt, or worse, to stick. Once your spear is stuck in an opposing shield, you cannot thrust, or parry. You could yank the spear out, perhaps killing the man behind you with your butt-spike, or ditch it. You would want to avoid this. With under-arm spear use, spearmen can prod. Over-arm spearmen cannot. Prods are very useful. By prodding an opposing shield off-centre, you can turn it, creating an opening for one of your neighbours to thrust through. By prodding at an enemy's shield, you can force him to pay attention to parrying you. You may not kill him this way, but you occupy his attention, and that has many uses. You can poke and prod about to work your spear into position, and then make a quick thrust. An over-arm spearman has to wait for his moment and then commit himself. If he hits a shield, which he often will, then he will very likely get his spear stuck.

Spears of the first rank or two could be pushed into enemies and enemy shields, and used to shove the enemy back. If the spearmen got very close, such that they were pushing with their shields against the shields of the enemy, then their spears would be impotent, and perhaps ditched in favour of swords. Conversely, if spears were used over-arm, then they could not be used for shoving the enemy back. Furthermore, I don't see how the two sides could close to shield-pushing range, without horrendous slaughter (and seeing this slaughter coming both sides would hang back). Once to shield-pushing distance, each side would have its spears above shield height, where they would be in the perfect position to thrust into the faces of the men opposite, and those men probably wouldn't be able to parry. The bloodshed would be very rapid indeed, which contrasts not just with common sense, but also with the literary records that talk of these contests lasting some considerable while.

The spear was a weapon, which was simple and effective. With it, men could combine their efforts against an enemy, and could keep that enemy at bay. A strong thrust was better than a cut at penetrating armour, and a spear was a good defence against cavalry. It was easy to make, and easy to learn to use. A limitation of the spear is that it is not a great weapon when used alone. A single swordsman has the advantage when facing a single spearman. Once he has closed with the spearman, he can hack away and the spear has become useless. The spearman can ditch his spear to get out a secondary weapon, but this takes time. Spears were not used other than in large formations. Once in close mixed melee, all ancient warriors preferred shorter weapons. In re-enactment fights, we found that it was worth bothering to use spears even if there were as few as three men in a line. The fights I took part in involved typically about a dozen a-side, hardly huge battles. Sometimes one side would charge effectively and win quickly, but most often the two sides would come together, and the spear-prodding stage would last for a few minutes (and several more if obstacles were involved). At some point, one side would see that it had the advantage. Perhaps the numbers of the enemy had been whittled down. Perhaps a gap in the line had been opened up, or one flank defeated. At this point, the side believing itself to be winning would ditch its spears and draw swords. Almost always, the only rational response to this would be to ditch spears as well, and then a fast and furious fight would start, and this would last for not many seconds.

Of course, since we were not actually killing people, nor fearing being killed, our re-enactments are not perfect duplicates of what actually took place in the past, but in terms of the wieldiness of weapons, and the effectiveness of low-level tactics, I feel that they are informative.
The simplicity of the spear is one of its strengths. Most spears were a very clean shape, so that they did not have hooks and such things that might catch on friend or foe. In ancient fighting, many men would have been killed while they were fumbling in some way. A man is vulnerable while his weapon is caught up in the clothes of his foe, and troops would want weapons that were not prone to this. In my re-enactment fights, I can only remember one instance of my fumbling with a spear during a fight. That was when I got it caught in a bush. By contrast, I can recall a hundred fumbles that occurred when I ditched my spear and raced to get some other weapon out. The swapping of weapons is a key moment. Spears do break. In re-enactment, most get broken when people fall on spears lying on the ground. In real fights, men would try to break their opponents' spears, and a strong blow from a sword could damage a spear's shaft. Formations of spearmen were often very deep, and many of the men near the back would never close to spear range. My belief is that a spearman at the front whose spear broke, could reach behind him and be fairly likely to have a replacement handed to him without much trouble.