Confederate General Leonidus Polk occupied Columbus and began erecting extensive fortifications in September 1861. In addition to the soldiers under his command, more than 13,000 at one point, over 10,000 African American slaves were present. Several of those who were enslaved were personal servants of officers, while all worked on building and maintaining earthen fortifications at Columbus. After Polk's Confederate army abandoned Columbus in March 1862, the site remained strategically important. The Union Army occupied Columbus, establishing a major supply depot and transshipment point where troops and supplies disembarked from riverboats and went south on the Mobile and Ohio Railroad, which had its terminus there, while a large garrison protected the river and rail transportation links and Columbus served as district headquarters for most of the war. Like all Union posts in the slave states, Columbus drew large numbers of African Americans seeking freedom, many arriving from the Mississippi River as soon as Union troops established themselves there. Union policy toward those known as contrabands was initially unclear, and some were returned to their masters before that practice was quickly stopped, though sheltering them then became a point of contention between Kentucky's political leaders and the federal government. The numbers seeking Union protection soon overwhelmed the resources and space at Columbus, and after Polk abandoned Island 10 to Union control, 1,000 former slaves were settled there in an agricultural colony. The colony remained in use throughout the war, and soon after African Americans were allowed to enlist, it was garrisoned by the 4th U.S. Colored Heavy Artillery. Throughout the war, but especially in 1862 and the first few months of 1863, African Americans who had fled to Union protection were used as casual labor by the army, loading and unloading riverboats and railroad cars in Columbus, building fortifications, and being sent as far as St. Louis when requested by Union commanders farther north. The records are unclear on whether they were paid for this labor. When the Thirteenth Amendment was ratified ending slavery, the acting district commander read the proclamation. After the war ended and the military base was decommissioned, Columbus became a district office for the Freedman's Bureau, where former slaves received legal advice, marriages were recorded, and assistance was given to build churches and schools.