7 Roman Battle Formations (+ Strengths & Weaknesses)

Ancient weaponry expert Dash Rendar goes over the most legendary formations used by the Romans

Co-authored by Dash Rendar and Elaine Heredia, BA

Last Updated: March 12, 2026 Fact Checked

A big reason that the Romans were able to conquer swaths of Europe, Asia, and Africa was how well-organized they were in battle. Some of their military formations, like the phalanx, were legendary for how efficiently they could decimate their enemies! But the Romans were also adaptable, so they developed new formations when the old ones didn't work anymore. Whether you're a Roman history buff, a Roman soldier cosplayer, or just someone who finds the Roman legion fascinating, this article is for you! In an exclusive interview with wikiHow, an ancient weaponry expert shared the most popular formations used by the Roman Republic and Empire, along with their strengths and weaknesses.

What formations did the Romans use?

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An illustration showing all 7 Roman formations.

Ancient weaponry expert Dash Rendar says the most common formations used by the Romans include the triplex acies, testudo, cuneus, and orbis. Here’s the breakdown:

Triplex acies: 3 rows of soldiers organized by experience
Testudo: Soldiers formed in a square shape with shields raised out and upward
Cuneus: A line of soldiers forming a wedge shape to break enemy lines
Orbis: A circle with shielded soldiers on the outside, used as a last-ditch effort

1

Phalanx

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A phalanx consisted of rows of soldiers standing close together with shields out. The Greeks may have invented the phalanx, but it was the Romans of the Early Republic who mastered it. For centuries, the phalanx was the most formidable military formation in the ancient world. Hundreds of soldiers would form into rows side-by-side, with only about 3 ft (0.91 m) of space between each row. The soldiers in the front row, closest to the enemy, would stab at the enemy from behind their shields with spears. They would also use their shields to push the enemy backwards. If one of them got killed, the soldier immediately behind them would move up into their place.^{[1]
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- Strengths: The rows of soldiers in the phalanx holding shields and weaponry were almost impenetrable from the front. They could also hold together while breaking through the enemy.
- Weaknesses: The phalanx was slow to turn, and its sides were vulnerable to speedy enemy cavalry (i.e., soldiers on horseback).
Meet the wikiHow Expert

Dash Rendar is an English warbow and ancient weaponry expert. He is passionate about sharing history and has 293k+ followers on YouTube and 417k+ followers on TikTok.

2

Cohort

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A cohort was a unit of soldiers that could combine or work with other cohorts. The Roman legion was made up of 10 cohorts. Each cohort was led by an officer called a centurion and made up of 480 troops, or legionaries.^{[2]
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- Strengths: Cohorts were relatively easy to organize and could take on large armies.
- Weaknesses: Cohorts were vulnerable to attacks by enemy cavalry, which meant they had to rely on their own cavalry units to protect them.
- Learn more about the Roman army's chain of command in our article, "Roman Military Ranks: A Beginner's Guide to the Legion"!

3

Triplex Acies (Triple Line)

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The triplex acies was formed from 3 lines of troops, organized by experience. As combat evolved from spears to swords, the Romans needed a formation that was smaller, faster, and more flexible than the phalanx. Enter the triplex acies (triple line), which Rendar says was the Romans’ default formation for most big, open battles. He explains that the formation has a checkerboard pattern with small maniples of about 120 men each. The younger soldiers were in the front, the principes (veterans) were in the middle, and the triarii (old professional soldiers with spears) were in the back to act as the “last stand” reserve.^{[4]
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Dash Rendar
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Expert Interview} Enemies didn't normally make it past the hastati and the principes, but when they did, the triarii would cut them to pieces.^{[5]
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- Strengths: The triplex acies could outlast small groups of enemies and fight across rough, hilly terrain. Individual triplex acies were smaller than phalanxes and could fight in different directions. Rendar adds that the gaps between units let tired lines swap out, or for rear soldiers to push through.^{[6]
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- Weaknesses: The triplex acies wasn't as effective against enemies with large-scale armies made up of multiple units.
- Later adaptations: Rendar notes that after Marius’ reforms (around 107 BC), the formation switched to bigger cohorts of around 480 men each, and 10 per legion. There were usually 4 cohorts at the front line, 3 in the second line, and 3 in the third line, with auxiliaries and cavalry on the flanks.^{[7]
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- Rendar adds that this update formation was mostly used on flat or open fields against infantry-heavy enemies, as it was perfect for grinding down opponents through sustained fighting.^{[8]
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- Battle examples: Rendar notes that it was used at places like Pharsalus in 48 BC, where Caesar held a reserve line back for a killer flank strike. However, it failed at Cannae in 216 BC when Hannibal’s cavalry wrapped around them, but Rendar says they quickly learned from it.^{[9]
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4

Testudo (Tortoise)

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Units formed a testudo by standing in a tight square and raising their shields. Testudo is Latin for "tortoise," and when you see this Roman legion formation in real life, you'll understand its name! In the testudo, Rendar says the front ranks would raise their shields vertically, the sides would angle their shields, and the rear ranks would hold their shields overhead, which created a giant turtle shell.^{[10]
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Dash Rendar
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Expert Interview} This clever use of shields protected the group from stones, arrows, and other missiles. It also allowed them to move (albeit slowly) across the battlefield.
- Strengths: Rendar says the testudo formation was super effective against arrows, javelins, slings, and anything else raining down on the soldiers.^{[11]
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  Expert Interview} The Romans could also use this formation in creative ways. They could set up their shields as a bridge or a ramp for other soldiers. They could also secretly carry special equipment like battering rams or ladders.
- Weaknesses: Rendar notes that testudo was slow and clunky for actual fighting, as it was hard for soldiers to see or swing, so it was mostly used for moving forward under fire or closing to walls.^{[12]
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  Expert Interview} It also only protected soldiers as long as they were moving or accomplishing their purpose. Once they actually had to engage in fighting, they had to break apart to use their weapons.^{[13]
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- Battle examples: Rendar notes that the formation was famously used at Alesia (52 BC, when Caesar’s men crawled up to the walls under Gallic arrows), at Masada (73 AD, mostly for ramps), and at various Parthian fights (where horse archers were a nightmare).^{[14]
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- Rendar adds that the testudo formation was mostly used for sieges, storming fortifications, and advancing across open ground with missile troops shooting at the soldiers.^{[15]
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- Check out our Ancient Roman Soldier Armor & What It Was Made Of" article to learn more about the scutum and other Roman armor parts!

5

Cuneus (Wedge)

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The cuneus was a triangle-shaped line for breaking through the enemy. The cuneus, or wedge formation, was less popular than the triplex acies or the phalanx, but it was still effective. Rendar explains that it was a dense, pointed formation where the strongest veteran soldiers were at the tip, with soldiers spreading out behind like an arrowhead. He says it concentrated a massive force at one point to punch through enemies, which then fanned out to widen the gap.^{[16]
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Expert Interview} While holding their shields in front of them, the soldiers would sweep into the enemy's ranks, creating a hole where the rest of the legion could pour in.^{[17]
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- Strengths: The cuneus was perfect for breaking the enemy's first line of defense. Rendar adds that it was primarily used to break up dense, disorganized lines (like wild Gallic or Germanic charges) and to crack a phalanx. He says it was good when the Romans needed a quick, decisive rupture.^{[18]
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- Weaknesses: The wedge formation would fall apart after the initial rush.
- Rendar notes that the cuneus formation was often used after a pila volley to soften the enemy.^{[19]
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- Battle examples: Rendar notes that it was used at Pydna (168 BC) against the Macedonians and at Watling Street (61 AD), where Suetonius used it to smash Boudicca’s huge but poorly coordinated British horde after a pila barrage.^{[20]
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Agmen Quadratum (Hollow Square)

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The agmen quadratum protected baggage and vulnerable troops in the center. In an agmen quadratum, or hollow square formation, a unit of soldiers would line up side-by-side to form a square shape. According to some sources, the square surrounded baggage, cavalry, or other vulnerable troops. This allowed the legion to move people and things across the battlefield while still protecting them.
- Strengths: The agmen quadratum enabled the legion to move its least defensible parts around the battlefield without leaving them out in the open. It also protected all sides.
- Weaknesses: If enemies targeted the agmen quadratum and broke through the guards, they would have an easy time picking off whomever (or whatever) was inside the square.

7

Orbis

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The orbis was a last-ditch effort to fend off enemies in a losing battle. If you were a soldier in the Roman legion, and your centurion told you to form into an orbis, chances are you were losing the battle. In an orbis (also called a circle or hollow square), Rendar says soldiers would form a 360° ring of shields outward (or a hollow square for bigger groups), where wounded, standard, and officer soldiers would be safe in the middle. He explains that it bought the Romans time when they were surrounded, ambushed, or retreating through hostile territory.^{[21]
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Dash Rendar
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Expert Interview} Unfortunately, this usually meant that the Romans had to fight to the death or surrender.
- Strengths: The orbis allowed the Romans to fight their enemies from all directions. Rendar adds that the formation could include archers or slingers firing from inside.^{[22]
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- Weaknesses: This formation was easy to surround, and it was only a matter of time before the Roman soldiers in the orbis would fall to their enemies, one by one.
- Battle examples: Rendar says the orbis was common in Gaul (like in the Sabinus and Cotta’s disaster in 54 BC), in frontier skirmishes, and in small detachments that got jumped.^{[23]
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- Rendar notes that the orbis formation was primarily used by cut-off units, during bad ambushes, or marches in enemy land that turned ugly.^{[24]
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