In the midst of the ruins of Chichén Itzá, there is a wall covered entirely in skull carvings known as a tzompantli (or skull rack, wall of skulls, skull banner, etc.). However this is just one version of a tzompantli. Another version consisted of a wooden construction that real skulls would be placed on after holes were drilled into them. Usually these skulls belonged to war captives or sacrificial victims. Skull racks have been found all throughout Mesoamerica and they have been dated ranging from 600 to 1250 AD (the epiclassic to post-classic eras), however a few are believed to have existed in the Zapotec civilization in 200 BCE (though the Zapotecs referred to it as a yágabetoo).
A typical tzompantli was a structure made up of vertically standing poles with horizontal poles interwoven to create a sort of checkerboard pattern. The skulls would either be on strings tied to these horizontal poles or slid onto the poles themselves. In the Maya regions, it was also common for the skulls to be impaled and stacked on the vertical posts. Other tzompantli are like the one at Chichén Itzá: a stone platform with rows of skulls carved into all sides upon which the real skulls would be displayed. The latter version was introduced to the Maya by the Toltecs along with large-scale human sacrifice. Some carvings on ball courts depict the losers of the ball game being beheaded and it is believed that those skulls were also displayed on the tzompantli, which is why the structures are now closely linked. This link is even displayed in the Popol Vuh through the imagery of Hun Hunahpu’s death. Hun was the father of the hero twins and was killed by the lords of Xibalba. The lords hung his severed head in a gourd tree next to a ball court as a way of gloating over their victory. This gourd tree was a symbol for the tzompantli as more skulls were depicted growing on the tree as if they were fruit.
Although the tzompantli at Chichén Itzá is one of the best preserved, the most renowned skull rack is located at Temple Mayor, Tenochtitlan in modern day Mexico City (known as the Huey Tzompantli). This tzompantli was discovered quite recently and is a great testament to how the Aztecs handled warfare. It is believed to have been built while the Aztecs were in the midst of the Flowery Wars and was used to display the skulls of fallen enemies turned sacrificial victims alongside the skulls of women and children sacrifices as Aztec sacrifice was very diverse. Several people have attempted to calculate the number of skulls on the platform, including one conquistador, but the estimated number varies widely from 60,000 to 136,000. The top of the structure used to hold a wooden structure tzompantli that is estimated to have held tens of thousands of skulls as well. Bernal Diaz Del Castillo even wrote an eyewitness account stating that when Cortes and his men were forced to retreat from Tenochtitlan, the Aztecs created a smaller tzompantli to display the skulls of the fallen Spanish men and even some of their fallen horses.