On several occasions during the third century BCE, the Roman Republic engaged in two-front conflicts while clashing with the Gauls and Etruscans to the north and also campaigning in Magna Graecia (the coastal areas of Southern Italy). When Rome was enmeshed in the Second Punic War against Carthage, Hannibal, formal ally of the Sicilian city of Syracuse, intrigued with Philip V of Macedon in 215 BCE, who promptly declared war on Rome. After the establishment of the Roman Empire and the consolidation of its frontiers under Augustus, the Roman legions regularly battled multiple enemies, most notably Germanic tribes on the Rhine and the lower Danube and the Parthian Empire in Syria and Mesopotamia. Various emperors, such as Septimius Severus and Aurelian forcibly led large armies to the opposite ends of the empire in order to deal with the various threats. Beginning in the third century the Roman - and its eastern successor the Byzantine Empire, trying to preserve its territories in Italy, struggled with the Sassanid Empire to the east for a period of more than 400 years. Large-scale incursions of Germanic tribes, such as the Goths and Hunnic raids in the west began during the fourth century and lasted for more than a hundred years.