Beginning in 610, under Generals Shahrbaraz and Shahin, the Persian army conquered Byzantine-controlled territories in Mesopotamia and the Caucasus. The Byzantine Empire could not offer much resistance to the invading Persians, with Heraclius himself needing time to implement a number of internal initiatives to ensure he could raise the necessary funds and troops for a renewed war against Khosrau II, the Sassanid king. In the next year, continuing their success, the Persian force overran Syria and eastern Anatolia, capturing Christian cities, such as Antioch and Damascus. Ostensibly, the Persian army could not travel much further into Byzantine territory without confronting a centrally-assembled Eastern-Roman army.