What does Martha Washington, Phillis Wheatley, and Mercy Otis Warren have in common?

Martha Washington corresponded regularly with Mercy Otis Warren, Boston historian and one of the leading lights of the Revolutionary era. Martha’s comments about the course of the war were an unusual foray into what was usually her husband’s exclusive domain.

Explanation:

adopted the practice of proskynesis, a persian court custom that involved bowing down and kissing the hand of others, depending on their rank.