Roman Army Playbook

Closed to Open Order


Scientific name:  Open Order

Colloquial names:  Closed to Open Order, Flare, Accordion

Scientific description:

Description: A formation that allows additional space between files and ranks. This formation was necessary for Roman legionaries to use their gladii hispanienses. Open order was approximately 182cm according to Taylor’s interpretation of Polybius’s somewhat problematic description (Polybius Ίστορίαι 18.30.5-6; Taylor “Visual Evidence for Roman Infantry Tactics” 106). Indeed, the inability to deploy in open order could impede tactical effectiveness and sometimes contribute to defeat (Caesar Bellvm Gallicvm 2.25.1; Polybius Ίστορίαι 3.116.10-11). In some situations Roman infantry employed an extra-open order to permit cavalry to pass.

Advantages: 1) permitted fresh troops to pass through; 2) permitted Roman legionaries to effectively use gladii hispanienses and pila; 3) helped to negotiate difficult terrain.

Disadvantage(s): 1) on level terrain, open order formations lacked the force of shock attacks by closer order formations, namely the Hellenistic phalanx.

Commentary: At Rusellae 302 BC, Tifernum 297 BC, and Aquilonia 293 BC, the Roman infantry deployed in extra-open order to permit cavalry to pass. At Cannae 216 BC, the Romans were able to contest the outcome until the line contracted (Polybius Ίστορίαι 3.116.10-11). At the Sabis 57 BC, the ambush by the Belgae significantly compressed the Romans. Caesar describes the soldiers as being a hindrance to themselves, which must refer to the crowding effect that deprived the legionaries of sufficient space to properly wield their swords (Caesar Bellvm Gallicvm 2.25.1).

Reference(s): Caesar Bellvm Gallicvm 2.25.1; Livy Ab Vrbe Condita 10.5.6-7, 10.14.15, 10.41.8-9; Polybius Ίστορίαι 3.116.10-11.

Category: Tactical Space

Battles: Rusellae 302 BC, Tifernum 297 BC, Aquilonia 293 BC, Cannae 216 BC, the Sabis 57 BC.

Number: 5*

Notes: Is this a good approach for close and open order formations, and other very common tactics, that is only include references in which its presence or lack of presence is highlighted? Perhaps also usual references to its presence or lack of presence.

* Open order was presumably used in every battle. Therefore this number includes references to battles in which the open order formation, or lack thereof, significantly contributed to the outcome.


Colloquial description:

 This involves the ranks of an infantry unit widening in width and/or depth, or “flaring” from closed rank formation, where soldiers are nearly shoulder to shoulder, to open rank formation where they are one to two arms-length apart.  This maneuver also includes adding space between ranks from front to rear.  This flare-outwards, or “accordion” play is used when the Roman infantry unit needs to expand their unit’s frontage to match the enemy’s front line frontage, and create space between soldiers for the discharge pila and to engage in combat. The “flare” from closed to open ranks could occur while the unit is stationary or in forward motion, and is initiated by the command of the centurion.  The flare could be executed even while running, immediately before engaging the enemy line.

Conversely, this maneuver can work in reverse, with soldiers moving from open order to closed order upon command.  This would be required, for example, to re-form the unit from an open offensive combat stance into a defensive posture such as a shield wall.  See also the Open to Closed order play.

Advantages:  Flaring from closed to open order was needed to create enough space between soldiers for them to wield spears and swords effectively.  Polybius tells us Roman troops in combat needed a minimum of three feet on either side (Polybius 18.30.5-6).  Opening ranks is required to enable effective hand-to-hand combat.  Flaring open on the run enabled the Roman unit to engage the enemy more quickly than stopping, opening ranks and then advancing.  It also facilitated the unit passing through narrow gaps between other units, gates, bridges and narrow spaces in terrain and then quickly flaring into fighting position.  This maneuver would be especially useful in the discharge of pila.  Throwing the pilum at a run after opening ranks greatly increased the force of pilum impact over a stationary throw.

The flare maneuver would greatly enhance the effectiveness of a hypothetical Roman Army play, the Piston, in which front line units withdraw and rest while a relieving unit advances to take their place on the front line.  The closed-to-open order play would enable the relieving Roman unit to quickly advance, moving around the withdrawing unit in closed order and then quickly flaring into open fighting position before discharging pila and engaging the enemy.  (See video animation on

The flare could also work in reverse, with soldiers moving from open ranks to closed ranks to facilitate unit withdrawal and create room for the relieving unit to “flare in” around them.

Disadvantages:  Running forward in closed ranks could be difficult, increasing the chance of over-anxious soldiers tripping each other.   Executing the flare on the battle line would be difficult and risky, as legionaries would need to be disciplined and well-drilled to execute this maneuver properly during a back-and-forth movement of units.


Open and closed formations have been a mainstay of armies from ancient times to modern.  Depictions of this maneuver are common in the literature, including the Manual Exercise as Ordered by His Majesty in 1764.


This US Military marching training video shows this drill in action.  One can easily imagine Roman Legionaries performing similar maneuvers.


Taylor, page 307-308, describes the flare maneuver as “flex forward”.




Korean riot police video mimicking ancient Roman tactics.

Note how the police units flare into open order while running towards the protestors, demonstrating how such a maneuver may have worked in ancient times


Primary (ancient) references:

Polybius Ίστορίαι 18.30.5-6



Number of times used:

Notes: Play #2 in Play Candidate List