Perhaps the World's Oldest Known Puzzle... Ostomachion!
Also known as Loculus Archimedius, Syntomachion and Stomachion, the Ostomachion is perhaps the world's oldest puzzle. It is attributed to Archimedes of Syracuse (287 BCE - 212 BCE).
The 14 pieces will make a square and also many other interesting shapes, with each shape requiring all the pieces.
It has been shown that each of the pieces has an area that is a rational fraction (a multiple of 1/48th) of the total area of the dissected parallelogram. Modern scholarship suggests that Archimedes anticipated combinatorics some 2,000+ years ago. Combinatorics involves finding the number of ways a given problem can be solved, subject to well defined constraints. Mathematician Bill Cutler determined in 2003 that there are 536 unique ways to assemble the square shape. Finding one way, is an extraordinary challenge!
There is an amazing story about how the Ostomachion puzzle was discovered on Archimedes' scrolls, the Palimpsest, which was cut up, written over and eventually recovered through a journey of more than two thousand years. William Noel presents the amazing story in this brief TedTalk found here: https://www.youtube.com/watch?v=VqtEppZmjfw
NOTE: Color schemes vary, and pieces may be different from colors shown in images.