Answer:
Both begin at important milestones based on the lives of their religions' founders
Step-by-step explanation:
The Muslim calendar begins the year in which Muhammad, prophet of Islam, had to flee from the city of Mecca to Medina, due to the persecution of his adversaries and established the first Muslim community. While the Gregorian calendar takes as its starting point the year in which Jesus was born. In Christianity Jesus is the Son of God made man.