Final answer:
Buddhism and Christianity both spread from their origins through trade routes and the efforts of merchants and missionaries, utilizing these networks to establish religious communities and expand their influence.
Step-by-step explanation:
One similarity in how Buddhism and Christianity spread from their original locations between 600 BCE and 600 CE is through the utilization of trade routes and the influence of merchants. As Buddhism spread across Asia, it followed major trade routes such as the Silk Roads, which facilitated the entry of religious ideas and missionaries into various regions. Similarly, Christianity made use of established trade networks in the Roman Empire and beyond to expand its reach. Both religions were carried by traders and missionaries who travelled these routes and established religious communities along the way, thus contributing to the gradual spread and adaptation of these belief systems beyond their points of origin.