Part of his plan was to coordinate his attacks with those of Yazdgerd III, the Sassanid emperor. In 635 Yazdgerd III had sought an alliance with Heraclius, marrying the latter's daughter (or granddaughter, according to tradition) Manyanh. While Heraclius prepared for a major offense in the Levant, Yazdegerd was supposed to mount a well-coordinated counterattack on his front in Iraq, while Heraclius attacked in the Levant. However, it was not meant to be. Umar probably had intelligence of this alliance, and started peace negotiations with Yazdegerd III, apparently inviting him to join Islam. When Heraclius launched his offensive in May 636, Yazdegerd, probably owing to the exhaustion of his government, could not coordinate with the Heraclian offensive, frustrating the plan.