The Aztec battle shield was a standard piece of military equipment utilized by almost every rank of the Aztec army.
Although arms and armor varied heavily and were often exclusive to specific military orders within the Aztec army, almost every soldier used some variation of the standard round shield. Most shields are depicted with feathered fringes hanging from the bottom, but this is not true in all cases. Curiously, certain ranks of soldiers are often depicted without these protective additions, while the ranks below and above them are.
The fringes themselves are often described as being made entirely out of featherwork, but this is doubtful. Depictions throughout nearly every codex show that the feathers on the very bottom were affixed to fringes of leather or hide. Certain shields (including one which is housed in Vienna today) include fringes which are made entirely with delicate featherwork, but these were used exclusively for ritual or display purposes and were far too fragile for the battlefield.
The shields could be constructed of woven cane or fire-hardened wood and some shields were even backed with cotton padding. The shields had two leather straps, where the user slid his arm through one and held the other in his hand. This allowed soldiers to affix the shields to their forearms, making them more secure and potentially allowing them to use both hands.
Because the shield was round, it was maneuverable in combat and less likely to get caught on something as it lacked corners. The shape of the shield also eased the use of swinging weapons such as the Macuahuitl or club, because again, it lacked corners which might accidentally catch a quickly swung weapon or otherwise prove burdensome.
In terms of protection, the shield could be used to parry incoming blows, stop a thrusting spear, and protect a soldier from incoming projectile fire. Stones from slings would likely be stopped completely and the shield was probably designed to stop arrows (although the arrow’s head may penetrate through the shield, it would probably stop short of complete penetration), but atlatl darts thrown hard and skillfully enough might have had the mass necessary to punch through the shield. The “Anonymous Conqueror” remarked that the Aztec shields were excellently made and required a “good crossbow” to shoot through them. Although it probably does not require mentioning, a Spanish matchlock would have no trouble punching through an Aztec shield.
Various patterns and designs were displayed on the front section of the shield and, in most cases, the design of the shield became more extravagant as a warrior progressed in rank.