Located in the southern portion of the Yucatan Peninsula, Calakmul sits within an ecological preserve of 819,000 acres, surrounded by a buffer zone of an additional 968,000 acres. Together, this vast territory makes up the Calakmul Biosphere Reserve. Since the decline of Calakmul and other nearby Mayan cities around 900 C.E., this area has remained undeveloped. It is, therefore, easy to understand why the site remained undiscovered by outsiders until 1931. At that time, Cyrus Longworth Lundell (1907-1994), a native of Austin, Texas, and one-time student at Southern Methodist University in Dallas, Texas, traveled to Campeche, Mexico, as a representative of the Tropical Plant Foundation in Washington, D.C., and the American chewing gun industry. While searching for chicle (natural gum) in an uncharted area of Campeche, he learned about the ruins of a lost Mayan city from locals, which he named Calakmul, “the city of two adjacent mounds.” This proved to be only the first of 16 ancient cities and other Mayan sites that he discovered. In 1932, Lundell informed Sylvanus Morley, then working at Chichen Itza, about the Calakmul site and his count of roughly sixty stelae there. Morely then organized the first Carnegie Institution of Washington expedition to the site in April 1932. This was followed by three additional surveys, ending in 1938, which resulted in the mapping of the city’s central area and the recording of 103 stelae.
Although the Calakmul Biosphere Reserve is largely uninhabited today, from 500 B.C.E. to roughly 1,000 C.E., it was home to a number of Mayan urban developments. The largest settlement was the city of Calakmul itself, which served as the seat of the Snake Kingdom -- called Kaan -- one of the most powerful Maya dynasties during the Late Classic Period. Represented by a snake head glyph, Calakmul fought with both Tikal and Palenque for regional dominance. With more than 6,200 buildings in a core area of 30 square kilometers (11.5 square miles), it was more densely settled than Tikal and had more stelae (115 to 130) than any other Maya city. Unfortunately, the stelae at the site are so badly eroded that archaeologists and epigraphers have been forced to piece together much of Calakmul’s history from records left in other areas.
Stela 51 at Calakmul is an exception to the general rule about eroded monuments at the site. Sylvanus Morley described it as “the most beautiful monument at Calakmul.” It was discovered with others at the base of Structure I by Cyrus Lundell in 1931 and first documented on the Carnegie Institution’s expedition to the site in 1932. The stela was stolen at some point in the 1960s, when it was cut into portable slabs, but later recovered. It now stands in the Maya section of the National Museum of Anthropology in Mexico City. 
The central portrait is that of the Calakmul king Yuknoom Took’ K’awiil, who erected the monument in 731 CE, making it one of the last of his reign. Yuknoom Took’ K’awiil ruled at Calakmul from 702 to 736, during which time he sponsored no fewer than twenty monuments at the site. Despite Calakmul’s defeat by Tikal in 695 CE, Yuknoom Took’ K’awiil was mentioned at Dos Pilas in 702 and Waka around the same time, suggesting that previous alliances remained intact. Even so, it seems likely that Yuknoom Took’ K’awiil’s reign probably ended in another defeat at the hands of Tikal’s great king, Yik’in Chan K’awiil in 736 CE.