Landing of the Pilgrims at Plymouth, December 21, 1620. Plymouth Rock is the traditional site of disembarkation of William Bradford and the Mayflower Pilgrims who founded Plymouth Colony in 1620. It is an important symbol in American history. Founded by a group of Separatists and Anglicans, who together later came to be known as the Pilgrims, Plymouth Colony was, along with Jamestown, Virginia, one of the earliest successful colonies to be founded by the English in North America and the first sizable permanent English settlement in the New England region. the citizens of Plymouth were fleeing religious persecution and searching for a place to worship as they saw fit. The social and legal systems of the colony became closely tied to their religious beliefs, as well as English custom.