In this video segment adapted from NOVA, learn about the writings found in ancient Maya codices—books written on bark. Although 16th-century Spanish priests burned many of these codices, four books and other structures featuring Maya hieroglyphs survived. Breakthroughs in efforts to decipher the Maya writings have shown that the Maya used a number system to precisely chart the 365-day solar cycle, predict solar and lunar eclipses, and track the complex orbit of Venus.