Proline Decorative Concrete Systems MD7400 4' Diameter Aztec Calendar Medallion Concrete Stamp. The Aztec Calendar is the calendar system that was used by the Aztecs as well as other Pre-Columbian peoples of central Mexico. Due to the high demand for this stamp, Proline has added this beautiful 4 ft. diameter stamp in their newest collection of Medallions. Beautifully detailed and artfully carved, this piece will be a stunning addition to any home or business. Easily colored with our new EZ-Accent water based acrylic stains.