From Wikipedia (English):
The problem called "as-Suli's Diamond" went unsolved for over a thousand years. In shatranj, the "queen" (counsellor) is a very weak piece, able to move only a single square diagonally. It is also possible to win in shatranj by capturing all pieces except the king.as-Suli gave the first move of the solution (1.Kb4) which was the same as Averbakh's solution; Averbakh was impressed with the obvious prowess of the Arab master.
as-Suli commented:“This ancient position is so difficult that there is no one in the world who would be able to solve it, except those I have taught to do so. I doubt whether anyone did this before me. This was said by al-Suli.”David Hooper and Ken Whyld studied this problem in the mid-1980s but were unable to crack it. It was finally solved by Russian Grandmaster Yuri Averbakh.
Solution (from the German Wikipedia) is in the comments. You have 1000 years, starting NOW...