This is a lesson plan for an activity in which learners, playing the role of archeologists, use math concepts about number bases to decipher the Dresden Codex, an ancient Mayan document. The lesson provides learners with historical background and exposure to how archeologists figure out what ancient documents mean. It also helps learners compare Mayan number systems (base 5) and modern number systems (base 10). It then leads them step-by-step through a series of activies to help break the code, with stopping points to discuss and investigate different ideas. In order to do this activity, learners should understand place value and number bases. Recommended for grade 5 and up.