For the period between 353 and 378, there is an eyewitness source to the main events on the eastern frontier in the "Res Gestae" of Ammianus Marcellinus. For the events covering the period between the 4th and the 6th century, the works of Sozomenus, Zosimus, Priscus, and Zonaras are especially valuable. The single most important source for Justinian's Persian wars up to 553 is Procopius. His continuators Agathias and Menander Protector offer many important details as well. Theophylact Simocatta is the main source for the reign of Maurice, while Theophanes, "Chronicon Paschale" and the poems of George of Pisidia are useful sources for the last Roman–Persian war. In addition to Byzantine sources, two Armenian historians, Sebeos and Movses, contribute to the coherent narrative of Heraclius' war and are regarded by Howard-Johnston as "the most important of extant non-Muslim sources".