Ense petit placidam sub libertate quietem is a Latin passage and the official motto of the U.S. Commonwealth of Massachusetts and the University of Massachusetts Amherst. The phrase is often loosely translated into English as "by the sword we seek peace, but peace only under liberty". The literal translation, however, is "she seeks with the sword a quiet peace under liberty." The "she" in question is the state. The passage itself is an excerpt from a longer quotation "Manus haec inimica tyrannis ense petit placidam sub libertate quietem," which means "this hand, hostile to tyrants, seeks with the sword a quiet peace under liberty."
It was written c. 1659 by English soldier-statesman Algernon Sidney, an opponent of Charles II and later executed for treason. The motto was first adopted by the Massachusetts General Court (i.e. the state legislature) and applied to the temporary seal of Massachusetts in 1775. On December 13, 1780 the legislature approved its application to the current Great Seal of Massachusetts.
The motto evokes the values of a peace-loving people, but a people who value liberty more than peace.