Forty years on, Al Jazeera examines three weeks of war from which both Arabs and Israelis claimed to emerge victorious. The first part of the series focuses on the build-up to the war and the role of an Egyptian double agent. It examines Egypt and Syria's lightning attack against an unprepared Israel as well as the Israeli response, the mobilisation of reserves and stabilisation of the Syrian thrust into the Golan Heights in a bloody tank battle in what became known as the 'Valley of Tears'. And it looks at the failure of an Israeli counterattack in the Sinai and the Egyptian consolidation of bridgeheads on the eastern bank of the Suez Canal.