Colonel Samuel Ryan Curtis, engineer, lawyer, and graduate of West Point, arrived in Mexico in July of 1846 as commander of the 3rd Ohio Volunteer Regiment to find a volatile and chaotic situation in occupied towns along the Rio Grande. American civilians of the lowest sort - men and women - mingled with Mexican townspeople, robbing, murdering, and raping. Neither civil nor military law made provisions for governing municipalities under such conditions. Nor was the U.S. military prepared for a struggle against Mexican guerrilla forces and desperate bandits. Colonel Curtis was a diary keeper, and this record of his experiences in Mexico gives a clear picture of his efforts to restore and maintain order under nearly impossible conditions: of death and suffering in his regiment from disease, not fighting, and of the tedium of army camp life. A reflective man as well as an educated one, Curtis was a keen observer. He documented social and economic circumstances, flora and fauna, and the weather, even as he chronicled political conditions and martial unrest. The resulting diary is a major contribution to studies of the Mexican War.