The Latin phrase, "semper fidelis," commonly shortened to "semper fi," means "always faithful" or "always loyal." It was adopted as the Marine Corps motto in 1883.
Before adopting Semper Fidelis as their motto, the Marine Corps had three mottos. The first motto, used before the War of 1812, was "With Fortitude." The second, "By Sea and By Land" was derived from that of the British Royal Marines. The third, "To the Shores of Tripoli," reflected the 1805 Marine victory in the Tripolitan town of Derna. In 1848, the third motto was revised to commemorate the capture of Mexico City.
In 1883, Semper Fidelis was adopted as the official Marine Corps motto. John Philip Sousa, then head of the Marine Corps Band, composed the official march of the Marine Corps, also called Semper Fidelis.