1. In 390 BC, an army of Celts attacked Rome, led by one Brennus capturing all of the city except for the Capitoline Hill which was successfully held against them.
2. In 279 BC, another army of Celts led by one Brennus invaded Macedonia and northern Greece. The following year they crossed the Bosporus and settled in a part of Asia Minor that came to be called Galatia.
Geoffrey of Monmouth also writes in his Historia Regum Britanniae about a personage named Brennius who conquers Rome. He probably created this character from the two Brenni of history.
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