A stone found in Guatemala carved by the Mayas some 1,300 years ago states that the ancient civilization's 13th "baktun" period - each of which lasts some 400 years - will end on Dec. 21, the second historical reference found regarding the ancient civilization's pending calendar change.

The find was announced this past week by Guatemalan and U.S. archaeologists who explained that they uncovered the stone last April at a dig being worked by students from Guatemala's Universidad Del Valle, Tulane and the University of Texas.

U.S. archaeologist David Stuart, one of the experts who announced the find, said that the carved steps on which the stone was found contains the longest Mayan text discovered to date in Guatemala.

This is the second reference ever found regarding the change in the Maya calendar. The other was uncovered at a site called Tortuguero in Mexico's Tabasco state, he said.

The stone was found among several panels making up the stairway found at the La Corona dig, an archaeological site uncovered in 1999 in Peten, a region in northern Guatemala bordering on Mexico and Belize, countries where - along with Honduras and El Salvador - the Mayan civilization once thrived.

According to Stuart, an epigraphist with the University of Texas, the stone makes reference to 13 Baktun, the Maya calendar based on 394-year periods, known as "baktuns," with each era made up of 13 cycles that added up to 5,125 years, and it was carved to commemorate the visit of the king of the Maya city of Calakmul.

The Maya calendar was divided into 20-year segments, each one called a "katun," and 20 of these periods made up one baktun.

King Yuknoon Yich'aak K'ahk, who was the most powerful Maya leader of the time, visited La Corona on Nov. 29, 696, some 13 centuries ago.

The written text on the stone refers to the end of 13 Baktun on Dec. 21, 2012, he said.

The glyphs carved on stone by the Mayas do not set forth any prophecies but rather record actual historical events from the 7th century, the U.S. expert said.

He said that the stones discuss events in the lives of the leaders and nobles of La Corona and list their names in order, and they also mention the queens who were part of the dynasty but were from Calakmul.

Stuart cited as an example the figure of a noble who is speaking with the king of Calakmul, which was a Maya capital, and that of another man who is seated on a Maya throne where feathers of quetzals (Guatemala's symbolic bird) are carved and glyphs refer to a war.

La Corona was a much smaller center than Calakmul, but it was strongly linked with that capital, Stuart said.

Guatemalan archaeologist Tomas Barrientos said that the stairway is made up of many panels but only 22 have been found after being discarded by looters. And just 12 of the panels have glyphs carved upon them.

"So, we feel that this is one of the longest Maya texts in history" because the panels form part of the frontal stairway of the building that experts believe was a residence, Barrientos said.

U.S. archaeologist Marcelo Canuto, who since 2005 has been coordinating the La Corona research project, said that the site was looted and the monuments bearing glyphs and other carvings were "the most desired and coveted."

Canuto said that La Corona was initially known as "Q" as a result of the looted panels that are on display in U.S., Australian and European museums.

In his opinion, the looters discarded the "ugliest" panels and took only the "prettiest."

"The looting shows that something important existed at La Corona," Canuto, the director of Middle American Research Institute at Tulane University, said.

"We've found many hieroglyphic monuments and we're trying to make a map of the site to see how it looked in the past, what its population was like and the use of animals they had to understand the social, political and economic life of the place," he said.

Guatemala is preparing to commemorate the end of 13 Baktun at several Maya archaeological sites.

The Mayan predictions for December 2012 were about the return of the god Bolon Yokte and not about the end of the world, experts say.

The Dec. 21, 2012, date found on Mayan glyphs led to speculation about Maya prophecies of the end of the world, prompting archaeologists and epigraphists to deny them.

In the Mayan cosmology, a cycle of creation was completed at the end of each era and then another began.

Bolon Yokote is a god associated with creation and war that participated in the start of the current era, which began on Aug. 13, 3114 B.C.

The idea that the pre-Hispanic civilization predicted the end of the world in 2012 has been popular in some New Age circles since the 1970s.