was crushed not by the Romans but by the rebellious Persian vassal king Ardashir I, who revolted, leading to the establishment of Sassanid Empire of Persia, which replaced Parthia as Rome's major rival in the East. Throughout the Parthian wars, tribal groups along the Rhine and Danube took advantage of Rome's preoccupation with the eastern frontier (and the plague that the Romans suffered from after bringing it back from the east) and launched a series of incursions into Roman territories, including the Marcomannic Wars. Late (180–476 AD) Migration period (163–378 AD) After Varus' defeat in Germania in the 1st century, Rome had adopted a largely defensive strategy along the border with Germania, constructing a line of defences known as limes along the Rhine. Although the exact historicity is unclear, since the Romans often assigned one name to several distinct tribal groups, or conversely applied several names to a single group at different times, some mix of Germanic peoples, Celts, and tribes of mixed Celto-Germanic ethnicity were settled in the lands of Germania from the 1st century onwards. The Cherusci, Bructeri, Tencteri, Usipi, Marsi, and Chatti of Varus' time had by the 3rd century either evolved into or been displaced by a confederacy or alliance of Germanic tribes collectively known as the Alamanni, first mentioned by Cassius Dio describing the campaign of Caracalla in 213 AD. In around 166 AD, several Germanic tribes pushed across the Danube, striking as far as Italy itself in the Siege of Aquileia in 166 AD, and the heartland of Greece in the Sack of Eleusis. Although the essential problem of large tribal groups on the frontier remained much the same as the situation Rome faced in earlier centuries, the 3rd century saw a marked increase in the overall threat,Grant, The History of Rome, p. 282 although there is disagreement over whether external pressure increased, or Rome's ability to meet it declined. The Carpi and Sarmatians whom Rome had held at bay were replaced by the Goths and likewise the Quadi and Marcomanni that Rome had defeated were replaced by the greater confederation of the Alamanni. The assembled warbands of the Alamanni frequently crossed the limes, attacking Germania Superior such that they were almost continually engaged in conflicts with the Roman Empire, whilst Goths attacked across the Danube in battles such as the Battle of Beroa and Battle of Philippopolis in 250 AD and the Battle