# Definition:Pythagorean Triangle/Historical Note

Pythagorean triangles were known to the ancient Babylonians in about $2000$ BCE.
The cuneiform tablet Plimpton $\mathit { 322 }$ list $15$ sets of Pythagorean triples.
It is also clear that the author of that tablet was also familiar with the fact, proved in Solutions of Pythagorean Equation, that the numbers $2 p q$, $p^2 - q^2$ and $p^2 + q^2$ always make a Pythagorean triangle.