The Mier Expedition was an offshoot of the Somervell Expedition, which was an unsuccessful military operation launched in November 1842 by a Texian militia against Mexican border settlements. It included a major battle at Ciudad Mier on December 26 and 27, 1842 which ended with a costly Mexican victory. The attack was partly in hopes of financial gain and partly in retaliation for the Dawson Massacre, in which thirty-six Texans were killed by the Mexican Army.