The Peace of Nisibis of 299, also known as the First Peace of Nisibis, was a peace treaty signed in 299 by the Roman and Sassanian empires, and concluded the Roman-Sassanian War of 296-299. The border established as a result of the treaty was maintained until the Second Peace of Nisibis of 363.
During the Roman-Sassanian War of 296-299, despite earlier successes in Mesopotamia, the Sassanian Shah Narseh was defeated by the Roman Caesar Galerius in Armenia in two successive battles. During the second encounter, the Battle of Satala in 298, Roman forces seized Narseh's camp, his treasury, his harem, and his wife. Galerius continued south through Sasanian territory and captured the Sasanian capital, Ctesiphon, before returning to Roman territory.
In 298, Narseh sent his ambassador Apharban to negotiate peace with Galerius and plead for the return of Narseh's family, however Apharban was dismissed and told to await an envoy with whom the Sassanians could conclude a treaty.Diocletian and Galerius met at Nisibis in the spring of 299 to discuss the terms of the treaty. Allegedly, Galerius proposed the submission and conquest of the Sassanian Empire, but this was dismissed by Diocletian whose more moderate terms were adopted and sent to the Sassanians. Sicorius Probus, the magister memoriae, was sent to convey the terms of the treaty to Narseh who had taken residence in Media.
The terms presented by Sicorius Probus included:
According to British historian George Rawlinson, Narseh was surprised by what he felt were moderate demands and agreed to all but the fifth condition of the treaty and it was subsequently withdrawn by Sicorius Probus. Another British historian Timothy Barnes gave a different account, noting that Probus stated that he had no authority to revise the agreement, leading Narseh to submit.
After the ratification of the treaty, Diocletian set about building and strengthening fortifications of the Limes Arabicus and Strata Diocletiana along the eastern border of the Roman Empire. Diocletian also increased the number of soldiers stationed along the border.