This is Michael Waski's original Timeline of Mathematics, which was developed specfically for the adolescent. It helps to tie together the entire curriculum through the years and between the sub-disciplines. Studing the history of mathematics is a critical component of the Montessori adolescent approach.
The Math Institute is currently revising and redesigning this timeline and will soon offer the new version here. If you are interested in this original version of the timeline, we are selling them while supplies last. Please note you will also need to cover the cost of shipment.