The Mier expedition, the last of the raiding expeditions from Texas into the area south of the Nueces River during the days of the Republic of Texas, was the most disastrous of the expeditions from Texas into Mexico. It developed out of the Somervell expedition, which captured Laredo and Guerrero. On December 19, 1842, Alexander Somervell, recognizing that his expedition had been a failure and concluding that a longer stay upon the Rio Grande might prove disastrous, ordered his troops to prepare to return home by way of Gonzales. Many of the men had reached the conclusion that there was little possibility of accomplishing their objectives of engaging the Mexican Army and of seizing and plundering Mexican towns, but they were so dissatisfied with the order to return home that they determined to separate from the command, cross the river, and attack the Mexican settlements to secure cattle and horses. Only 189 men and officers obeyed the order to return; five captains and most of the men refused to do so. Constituting what is known as the Mier expedition, they moved down the Rio Grande to a convenient campsite and selected William S. Fisher as their commander. Some wanted revenge and retaliation; many sought adventure; the leaders were nearly all political opponents of Sam Houston.
The expedition set out on December 20. Forty men under Thomas J. Green floated downstream in four vessels captured near Guerrero. A small group of Texas Rangers serving as a spy company under Ben McCulloch operated along the west bank of the river; the main body of men under Fisher went down the east side. On December 22 the 308 Texans reached a point on the east bank of the Rio Grande opposite Mier, and McCulloch's spy company was sent to reconnoiter the town. They found that Mexican troops were assembling along the river, advised Fisher against crossing, and abandoned the expedition when their advice was not heeded. Thereupon, John R. Baker, sheriff of Refugio County, succeeded to the command of the spy company. Leaving a camp guard of forty-five men, Fisher and the remainder of his men crossed the river on December 23 and entered Mier without opposition. A requisition for supplies levied against the town was fulfilled by late afternoon, but there were no means for transporting the goods to the river, and the Texans had no desire to carry the goods on their backs. When the alcalde promised to have the supplies delivered the next day to the Texas camp, the Texans withdrew from Mier, taking the alcalde with them to guarantee delivery of the supplies. All day on December 24 the Texans waited in vain for delivery of the goods. During the morning A. S. Holderman, who had crossed the river to look for horses, was captured by a small detachment of Mexican cavalry. His journal revealed to the Mexicans the size, character, and organization of the Texan force. On December 25 Fisher learned from a captured Mexican that Gen. Pedro de Ampudia had arrived at Mier and prevented delivery of the supplies. The Texans decided to go after their rations. On the afternoon of December 25 a camp guard of forty-two men under Oliver Buckman was posted, and 261 Texans crossed the Rio Grande once more, attacked Mier, and fought until the afternoon of December 26, outnumbered almost ten to one. Mexican losses were 600 killed and 200 wounded as against thirty Texans killed and wounded; but the Texans were hungry and thirsty, their powder was almost exhausted, and their discipline had begun to crack. Ampudia adopted a suggestion of sending a white flag to the Texans and demanding their surrender; the ruse was successful.
The Texans later claimed they had surrendered as prisoners of war, but no terms of capitulation were signed until after their arms had been grounded and the terms then stated that they would be treated with "consideration." Later President Houston stated that the men had acted without authority of the government, leaving the impression that they were not entitled to treatment as prisoners of war unless the Mexican government wished to assume that obligation. Warned by two of their comrades who escaped from Mier after the battle, the Texan camp guard, with the exception of George W. Bonnell and a man named Hicks, avoided capture and retreated into the settled area of Texas. The captured Texans were sentenced to execution, but on December 27 Ampudia had the execution decree reversed. The able-bodied prisoners were marched through the river towns to Matamoros, where they were held until ordered to Mexico City. En route to the capital they planned their escape frequently. Finally, at Salado, on February 11, 1843, a successful break was carried out. For seven days the Texans headed towards the Rio Grande, but in trying to pursue a circuitous route through the mountains during the dry season they became separated and lost. After extreme suffering, they surrendered singly and in small groups to Mexican troops sent in pursuit; in the end only three members of the expedition made good their escape to Texas. The 176 recaptured Texans were returned to Salado. Upon learning of the escape, Antonio López de Santa Anna ordered that those who had fled be executed, but Governor Francisco Mexía of the state of Coahuila refused to obey the order, and the foreign ministers in Mexico were able to get the decree modified. The government then ordered that every tenth man be executed. The seventeen men who were selected for execution in what is known as the Black Bean Episode were blindfolded and shot. Ewen Cameron, leader of the break, failed to draw a black bean of death but was later executed by special order of Santa Anna. During the months of June, July, and August 1843, the Texans did road work near Mexico City. In September they were transferred to the Perote Prison where the San Antonio prisoners whom they had set out to liberate were being held. A few of the Mier men escaped while stationed in the vicinity of Mexico City, others tunnelled out of Perote and succeeded in reaching home. A few of the wounded who had been left at Mier recovered, bribed the guard, and effected their escape. Many of the men died in captivity from wounds, disease, and starvation. From time to time a few of the prisoners were released at the request of certain officials in the United States and others at the request of foreign governments. The last of the Mier men were released by Santa Anna on September 16, 1844.