Archaeologists excavating a pyramid complex in the Guatemalan jungle have uncovered the earliest example of Mayan writing ever found, 10 bold hieroglyphs painted on plaster and stone.

The 2,300-year-old glyphs were excavated last April in San Bartolo and suggest the ancient Maya developed an advanced writing system centuries earlier than previously believed, according to an article published Thursday in the journal Science.

The glyphs date from between 200 B.C. and 300 B.C., and come from the same site in the Peten jungle of northern Guatemala where archaeologist William Saturno found the oldest murals in the Mayan world in 2001. Radiocarbon tests indicate the writing is 100 years older than the murals depicting the Mayan creation myth.

The glyphs, thin black paintings on off-white stucco, lay in a plastic tub in a laboratory in an old house in the colonial city of Antigua on Thursday as archeologists cleaned and cataloged other stones from the San Bartolo site.