The Proving Grounds of Gyras were the site of vicious blood feuds dating from the Aeon of Strife, virtually flooding the proving grounds with the life force of thousands of protoss warriors. The feuding there ended when Khas used the power of the khaydarin crystals to destroy the arena there. The ruins forever serve as a reminder of what transpired in the past.
Despite the destruction wrought, the Proving Grounds still serve a purpose. Although Khas strove to bring unification and enlightenment to his people, he also knew that some disputes would still demand resolution through force. Therefore, the ruins were sanctified as an arena of honor, and those who seek to settle personal matters come back to Gyras to prove their mettle in battle.
The area appears as a multiplayer map in StarCraft, supporting up to four players.
1998-10-23. Proving Grounds. StarCraft Compendium Map Archives.