Complex sentence: He had a paternal half-brother called Marcus Claudius Ummidius Quadratus, from his father's first marriage, who was adopted by the Roman Consul Marcus Ummidius Quadratus Annianus, a nephew of the Roman Emperor Marcus Aurelius.
Split into simpler sentences: He had a paternal half-brother called Marcus Claudius Ummidius Quadratus, the child from his father's first marriage. His paternal half-brother was adopted by the Roman Consul Marcus Ummidius Quadratus Annianus, who was the nephew of the Roman Emperor Marcus Aurelius.