Complex sentence: During the Roman period, they successfully subdued the Gauls in 52 BC and began developing Cenabum which they named Aurelianis and also began building the city of Caesarodunum, now Tours, from AD 1.
Split into simpler sentences: During the Roman period, they successfully subdued the Gauls in 52 BC and began developing Cenabum, which they named Aurelianis. They also began building the city of Caesarodunum, now Tours, from AD 1.