Abner Hosmer was one of the Acton minutemen who was killed at the battle of the North Bridge in Concord, April 19, 1775.  The tombstone reads:

Momento mori

Here lies the Body of Abner Hosmer son of Deacon Jonathan Hosmer & Mrs. Mary his wife who was killed in Concord fight April 19th 1775 In defence of the just right & Liberties of his Country being in the 21st year of his age.