The Roman Testudo: Shield Roofs from Carrhae to Modern Riot Lines

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The testudo, or tortoise, turned a block of Roman legionaries into a moving armored box. It depended on the scutum, a curved shield about four feet tall and two and a half feet wide, built of glued wooden strips covered in canvas and leather with an iron boss, weighing 15 to 20 pounds. The front rank overlapped shields from shin to eye, the flanks and rear faced outward, and the inner ranks rested their shields on their helmets so the weight and impact ran down the spine into the ground, overlapping like roof shingles. Cassius Dio, describing Mark Antony's campaign of 36 BC, claimed the roof was so solid that horses and carts could be driven across it to cross a ravine.

The formation had a fatal weakness: it was slow, blind, and useless for hand-to-hand fighting. At Carrhae in 53 BC, Parthian horse archers forced the Romans into the testudo, then armored cataphracts charged into the packed ranks. Its real home proved to be the siege, where the threat came from above. The episode follows the shield roof through Muslim, Viking, Frankish, crusader, and Byzantine use and into modern crowd control.

• In Antony's Parthian campaign, the front rank knelt so the formation became a slope that deflected arrows rather than absorbing them.
• At Carrhae, breaking formation to fight the cataphracts left gaps that the horse archers exploited, a trap with no good answer.
• Muhammad's forces used a shield roof at the siege of Ta'if in 630, and crusaders used one at Nicaea in 1097.
• At Tobna in modern Algeria in 906, Abu Abdallah al-Shi'i used the formation, called the dabbaba or crawler, to shelter sappers undermining the walls.
• Riot police formed the same interlocking roof in Belize in 2005 and in Kyiv during the 2014 Euromaidan protests.