The “roll-up shield” is a shield that was ostensibly used by Aztec soldiers.
The writings of the conquistador Bernal Diaz Del Castillo describe many aspects of Aztec life in some detail. When he and his fellow soldiers toured a fully stocked Aztec armory during their stay in Tenochtitlan, Castillo described the arms and equipment found inside. One particularly interesting piece of equipment he described was a shield which was “so cleverly constructed” that it could be rolled up and stored when not in use, but was large enough to protect the entire body when it was unrolled.
No original depictions of this shield actually exist, but some guesswork can be done about its construction. Anthropologist Ross Hassig argues that, perhaps, the long “fringes” or leather straps which often hang from the bottom of standard Aztec circular shields might have made the typical protective shield appear to be a different type. In other words, Hassig suggests that Castillo might have misinterpreted or improperly described an Aztec round shield. Personally, I would argue that Castillo had enough contact with native armaments to be able to differentiate between the specific types, especially in regard to something as simplistic as a shield.
In addition, Castillo describes the shield as being large enough to cover the entire body. Featherwork or leather fringes of that length are cumbersome, easy to tangle, and lose their protective capability as the distance from the shield increases, making that scenario unlikely.
According to Hassig, Aztec archer formations have been protected by shield bearers under certain, limited circumstances. The typical Aztec round shield is small enough to allow freedom of movement during hand to hand combat, but large enough to protect the user from projectile fire. It is not, however, large enough to protect both the user and another unshielded individual. Because of this, it would make some logical sense for the Aztecs to deploy and use larger shields under certain circumstances. The fact that these shields could be “rolled up” allowed a greater number to be carried without compromising the efficiency of a mobilized army.
The shield would have been constructed of strong, durable, soft material such as interlaced wickerwork or perhaps segmented wood was used. A combination of the two might have been most effective. In any case, a removable wooden “spine” could have been used to help the shield maintain its rigidity during use.
Obviously, this is all mere conjecture on my part. The fact that no original representations of these shields exist indicates that they were seldom used by Aztec soldiers when they engaged the Spaniards. This could mean that they were used on specific campaigns, during limited circumstances, or perhaps they were used to protect soldiers during city assaults or sieges. Another possibility is that these shields were used in the past, but were rendered outdated and unused by the time that the Spanish arrived. I doubt that we will find an answer any time soon.