Among the Greek sources on the history of Byzantium in the period preceding the Arab conquest, the work of Theophylact Simocatta occupies one of the first places. His Ίστορίαι is an important monument for characterizing a whole period in the history of Byzantium, when it fought against the advance of the Slavs and Avars on the Balkan Peninsula, fought fiercely with Iran for its eastern borders, and experienced deep internal turmoil. Simokatta's work is of great interest for its rich factual material relating to the Slavic and Turkic peoples and the situation in the Middle East.