Testudo formation

In Ancient Roman warfare, the testudo or tortoise formation was a formation used commonly by the Roman Legions during battles, particularly sieges. Testudo is the Latin word for "tortoise". The Greek term for this formation is "chelone" and during the Byzantine era, it seems to have evolved to what military manuals of the era call the "foulkon".

In the testudo formation, the men would align their shields to form a packed formation covered with shields on the front and top. The first row of men, possibly excluding the men on the flanks, would hold their shields from about the height of their shins to their eyes, so as to cover the formation's front. The shields would be held in such a way that they presented a shield wall to all sides. The men in the back ranks would place their shields over their heads to protect the formation from above, balancing the shields on their helmets, overlapping them. If necessary, the legionaries on the sides and rear of the formation could stand sideways or backwards with shields held as the front rows, so as to protect the formation's sides and rear; this made the formation slow and they covered very little ground.

Plutarch describes this formation as used by Mark Antony during his invasion of Parthia in 36 BC:

Cassius Dio writes about the testudo when describing the campaign of Mark Antony in 36 BC:

The testudo was used to protect soldiers from all types of missiles. It could be formed by immobile troops and troops on the march. The primary drawback to the formation was that, because of its density, the men found it more difficult to fight in hand-to-hand combat and because the men were required to move in unison, speed was sacrificed. As "foulkon", it played a great role in the tactics employed by the Byzantines against their eastern enemies.

The testudo was not invincible, as Cassius Dio also gives an account of a Roman shield array being defeated by Parthian cataphracts and horse archers at the Battle of Carrhae:

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