In the midst of the ruins of Chichen Itza, there is a wall completely covered with skull carvings, known as a tzompantli (or skull rack, wall of skulls, banner of skulls, etc.). The tzompantli in Chichen Itza is dedicated to the dead and can be found at various Maya archaeological sites. It is one of the oldest tzompantlis ever discovered. Another version consisted of a wooden structure on which real skulls were placed after holes were drilled into them. Usually, these skulls belonged to prisoners of war or sacrificial victims. Skull racks have been found throughout Mesoamerica and date from 600 to 1250 AD (the Epiclassic and Postclassic periods), although it is believed that some existed in the Zapotec civilization as early as 200 BC (although the Zapotecs called them yagabetu). Archaeologists have discovered buried Chaac Mool figurines in the Tzompantli at Chichen Itza, as well as offerings made from skulls and a broken ring from the ball court. A typical tzompantli was a structure consisting of vertically standing posts with horizontal supports woven together to create a kind of checkerboard pattern. Skulls were either hung on strings tied to these horizontal poles or placed directly onto the poles themselves. In Maya regions, it was also common to impale skulls on stakes and mount them on vertical posts. Other tzompantlis resemble the one at Chichen Itza: a stone platform with rows of skulls carved on all sides, on which real skulls were meant to be displayed. This latter version was introduced by the Maya-Toltecs along with large-scale human sacrifices. Some depictions on ball court walls show the decapitated losers of the ball game, and it is believed that these skulls were also displayed on tzompantlis, which is why these structures are now closely associated.

This reference even appears in the "Popol Vuh" through images of the death of Hun Hunahpu. Hun was the father of the Hero Twins and was killed by the lords of Xibalba. The lords hung his severed head on a gourd tree next to the ball court to gloat over their victory. This gourd tree was a symbol of the tzompantli, as the tree was depicted with many skulls growing as if they were fruits.

The first and most striking example is the Huey Tzompantli (Great Skull Rack), located in the Aztec capital of Tenochtitlan and described by early conquistadors. There were at least five other skull racks in Tenochtitlan, but they were apparently much smaller. The most famous skull rack is located in the Templo Mayor, Tenochtitlan, in modern-day Mexico City (known as Huey Tzompantli). This tzompantli was discovered quite recently and is an excellent testament to how the Aztecs waged war. It is believed to have been built when the Aztecs were in the midst of the Flower Wars and was used to display the skulls of defeated enemies who became sacrifices, along with the skulls of sacrificial women and children, as Aztec sacrifices were very diverse. Several people have tried to count the number of skulls on the platform, including one conquistador, but the estimated number varies widely from 60,000 to 136,000. At the top of the structure was once a wooden tzompantli structure, estimated to have held tens of thousands of skulls as well. Bernal Díaz del Castillo even wrote an eyewitness account that when Cortés and his men were forced to retreat from Tenochtitlan, the Aztecs created a smaller tzompantli to display the skulls of fallen Spaniards and even some of their fallen horses.

The Tzompantli or Skull Platform at Chichen Itza is one of the best-preserved structures of this type. This large T-shaped platform is decorated with panels adorned with skulls, and its sides feature bas-reliefs in the shape of skulls. In total, more than 500 bas-relief skulls have been found on the walls. It is a huge rectangular platform 60 meters high and 12 meters wide. At the base are three panels decorated with skulls and separated by stucco molding. This monument is the most vivid evidence of the practice of human sacrifice carried out by the rulers of Chichen Itza for religious and military purposes. On the walls of the Tzompantli platform are beautifully carved reliefs depicting four different scenes. The main scene is the skull rack itself; others depict scenes of human sacrifice; eagles devouring human hearts; and skeletonized warriors with arrows and shields.

Sources:

https://www.chichenitza.com/tzompantli#:~:text=The%20Tzompantli%20of%20Chichen%20Itza%20is%20a%20great%20rectangular%20platform,with%20another%20row%20of%20skulls

https://historicalmx.org/items/show/91