For the first two centuries of its existence, Rome was overwhelmingly powerful, and its political institutions were strong enough to survive even prolonged periods of incompetent rule. Trouble was afoot on Rome's borders, however, as barbarian groups became more populous and better-organized, and as the meritocratic system of the “Five Good Emperors” gave way to infighting, assassination, and civil war. At the same time, what began as a cult born in the Roman territory of Palestine was making significant inroads, especially in the eastern half of the Empire: Christianity.
Image Citations (Wikimedia Commons):
Augustus Caesar - Till Niermann
Colosseum - Andreas Ribbefjord
Empire 117 CE - Eleassar
Roman Legion - Ursus