Our tour guide from Calica to Tulum, Ruben was well informed and a real gem on the tour. The one thing that he emphasized was that the Mayan's have not dissappeared, just there knowledge. Most all books from the time were destroyed by european explorers, so the extent of their learning can only be assumed from the remaining buildings and stone carvings. Their written language is estimated to date back 3000 years B.C.