Final answer:
The spread of Christianity in the Roman Empire was aided by road systems, a common language, and its appeal to the poor. However, it was not universally accepted by the Roman rulers initially, which made their rule a challenging environment for Christians.
Step-by-step explanation:
The factors that aided the spread of Christianity throughout the Roman Empire include the road systems, a common language, acceptance by Roman rulers, and its appeal to the poor. The Roman road systems and the common Greek and Latin languages facilitated communication and diffusion of ideas, including Christian teachings. However, the option that does not fit is 'acceptance by the Roman rulers'. In fact, Roman rulers systematically persecuted Christians for centuries before Emperor Constantine's Edict of Milan legalized Christianity in 313 AD.
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