According to this answer to this question (Is Chaturanga/Shatranj an early form of chess or is this altogether different?):
Chaturanga is the ancient game that gave birth to board games chess, shogi, makruk, xiangqi and janggi. I believe Chaturanga is the same game as Shatranj or got only slightly varied while moved from India to Sassanid Persia.
So, I understand that the earliest form of chess in Persia and the Middle East was called Shatranj and derived from Indian Chaturanga.
What are the rules of this early form of chess?