There’s a religious and historical reason why Sunday is the first day of the week. Historians believe both ancient Egypt and Rome had a role to play in this fact. In ancient Egypt, Sunday was seen as the “day of the sun” and was spent honoring the sun god, Ra. Worship was seen as a suitable way to start a new week. Ancient Rome may have also contributed to Sunday as the first day of the week. The Romans believed that the week started with the sun (Sunday) and moon (Monday) and ended with Saturn (Saturday).