Hoplites (pronounced hop-li-tes, not hoplights) were ancient Greek Citizen soldiers. In your average ancient Greek City State (Polis), every citizen who could afford weapons was required to buy weapons and practice with them. Poor people either became rowers manning oars or Peltasts, light soldiers armed with slings, bows and Javelins to harass enemy formations or they were shunted to the rear of a formation leaving the richer and more well equipped soldiers to be up front and bear the brunt of the enemy attack. Rich people became light cavalry who scouted things out and chase down Peltasts and fleeing soldiers. Middle class people became Hoplites, the main force of the Army. When a war was declared or an enemy decided to attack some of these guys would gather up, vote on a leader and march off to war.
The main exceptions to this rule were the Spartan Spartiates and the Sacred band of Thebes, both being forces of professional full-time Hoplites. For Spartans, every single citizen was expected to be a full-time professional soldier trained from childhood (they had LOTS of slaves to do all the other work), allowing them to be widely feared despite not having the biggest armies. The Sacred Band, meanwhile, was an elite shock unit of 150 male couples - the logic being that you'd fight harder if your lover was in the same unit as you. Apparently it worked, as they were able to go toe-to-toe with Sparta, and it took the new Macedonian armies to defeat them. In both cases, they held the advantage because, as professional soldiers, they were disciplined as hell, which is pretty crucial when you're playing the world's deadliest game of chicken. Most battles between hoplites were rarely to the death; the battle would end as soon as one side lost their nerve and broke ranks to rout, rarely resulting in more than 20% casualties. If your side doesn't flinch and just walks right up to the enemy, there's a good chance that the enemy will just chicken out and run.
Greek Weapons and Tactics
Hoplites got their name from the Hoplon, a round wooden shield with a bronze covering about a meter in diameter. Their main weapons were a three meter long spear, a short sword, and a dagger. Hoplites usually wore bronze helmets and had breastplates made of leather, padded linen or bronze, as well as having grieves and bracers. Poorer hoplites had lower quality armor than their better off counterparts.
Hoplites fought in tight square formations called phalanxes, each man protecting the other two guys to his side while being highly resistant to the projectiles since the greeks did not have longbows or high powered crossbows that were man portable. Running into a phalanx meant running into a wall of spears held by well defended guys, and was generally considered suicide unless you were in a bigger Phalanx. In phalanx on phalanx fights, they would ram into each other until one side broke formation either through casualties or a few guys panicking and deciding to run away. If that happened the rest of them would very soon run away as quickly themselves as possible and they would have lost. That was how most battles ended and usually one side broke before more than 10% losses were inflicted. As such two most important qualities for hoplites are discipline and fortitude.
Macedonian Weapons and Tactics
However the masters of Phalanx warfare were the Macedonians under king Philip II and his son son Alexander the Great. Under Philip the Macedonia Phalanx did away with the Hoplon and instead doubled the size of the spear to six meters, thus turning it into a pike, they also wore lighter armor for more speed. These longer spears allowed men in the ranks behind the front row to also bring their spears to bear, meaning that if an enemy got past the first spear, he still had four more spears to get past to even reach the man in the first row. The Macedonia's were armed with a Kopis short sword if, somehow, the enemy got though the wall of pike heads to get to them. The difference were so great that the Macedonia's pikemen were not called Hoplites, but "Sarissaphoroi", named after there weapon the Sarissa, but most modern accounts just call them pikemen since that's what they are.
Much more importantly than better gear, however, the Macedonian Phalanx was not used as the only formation on the field but as a part of a wider formation in an antique demonstration of combined-arms tactics. Under Macedonia tactics the heavy phalanx would lead the way and hold the enemy in place while heavy cavalry in wedge formation would swing into the flank(s), break the enemy formation and allow the Hypaspists (smaller formations of elite infantry who were armed like greek hoplites who were stationed to either side of the Phalanx to defend its flanks) to charge forward and break the enemy once and for all. The Hypaspists themselves were supported by lighter infantry and/or bowmen and slingers on their sides whose job was to keep the enemy from flanking the heavy hitters.
Additionally the Macedonians were fast. The Macedonian pike men marched in a loose formation, then came together only when the enemy was near, they wore lighter armor and this was coupled with a minimal baggage train. This meant that the Macedonians could cover ground much faster than other armies, and they could often make an enemy surrender simply by arriving to a battlefield days before they were expected.
This combined forces tactical approach would later be perfected after being abandoned for over 1500 years by the Spanish who combined pikemen with early handguns, combining firepower to harass the enemy at range and scare away its outriders with the fearsome wall of pikes to keep the heavy hitters at bay. The Spaniards used their tercios to dominate European land warfare until cannons precise enough to reliably hit the infantry squares were fielded and compact formations became suicidal.
The Problem with Hoplites
There are four, or rather five, issues with Hoplites. First is like any nonprofessional army there are some times of the year they just will not fight, namely fall when the citizens need to go home to harvest crops or starve (or in the case of Sparta, who were professional soldiers, they couldn't go too far away from home to prevent slave revolts, as slaves were always in higher abundance than Spartiates even when all Spartiates were at home). The second issue with Hoplites is that the Phalanx has trouble keeping formation over rough ground, and without the formation a Hoplite is almost completely out matched by most other infantry types since the other guy can just get within the spears reach and use his axe to split a Hoplite in half. The third issue with the Phalanx is that it disintegrates if flanked, the spears become useless and the tightly packed formation means it's hard for the men to escape or readjust facing to combat the new threat (think about how hard it is to swivel a pole taller than you while trying not to bump into a dense crowd). Fourth issue is that due to the phalanx being designed around not only protecting yourself but also the one on your left with your shield (hence their size), the right side of the phalanx is vulnerable as naturally, the guy on the right only has his own shield to protect himself with. The fifth really big problem with the Hoplites, and their biggest issue, was nothing with the Hoplites themselves, and more their commanders. After Alexander the Great's 8 year whirlwind tour of the known world, the Macedonian combined arms approach to warfare was dropped in favor of just having big phalanxes, and since everyone was just using Phalanxes this was not a problem. But when the Roman manipular system of battle (80-man companies who can make independent calls on the battlefield famously called "A phalanx with joints") came into fruition, along with the revolutionary quinqux formation (checkerboard formation that allows reserves to fill in the gaps created by lines, and for entire units to cycle through with the reduced risk of fatigue), the unsupported phalanxes found themselves outmaneuvered and outmatched.
Hoplites in Speculative Fiction
Despite the issues with hoplites in real life, their badass aesthetic has led to continued appearances in multiple /tg/-related properties.
- The Unsullied from A Song of Ice and Fire were armed like Hoplites and fought in a Hoplite manner, though instead of being citizen militia they are Eunuch slaves trained from childhood be unflinchingly loyal to their masters and extremely disciplined. The Legions of New Ghis are closer to Hoplites, being armed in the same way but being citizen soldiers.
- The Phalanx Soldier is a Fighter Archetype from Pathfinder which tries to emulate real hoplites' style of combat by allowing the fighter to wield a two-handed spear or polearm one handed while using a shield. This makes the fighter very good at striking enemies before they even have a chance to attack him in close combat while staying very well defended.
- In Warhammer 40,000, the Titans of the Adeptus Titanicus are protected from enemy infantry by a special division of Skitarii called the Secutarii Titan Guard. One of the troops they field are called Secutarii Hoplites, which are brainwashed cyborg-soldiers with mag-inverter shields and arc lances, making them formidable opponents to any who might try to loot a fallen titan.
- Additionally, pretty much any spec fiction setting that involves Greeks or Greek-inspired aesthetics is almost guaranteed to have at least a few elements of hoplites in their soldiery. In particular, Amazons are often portrayed with this aesthetic when they're not being portrayed as savages who live in the jungle.
- Both the Arkadia and Odyssey of the Dragonlords settings have a Hoplite themed subclass for the Fighter in Dungeons & Dragons 5th Edition, with Odyssey also having one for the Monk as well.