Answer: To escape slavery. 

Henry Brown was born in the early 1800s at Hermitage, a plantation in Louisa County, Virginia. Around the age of fifteen, Henry was separated from his family and sent to work for William Barret of Richmond, Virginia.  A few years later he married a woman named Nancy, and the couple, living as slaves of separate masters, had several children. In 1848, Nancy was sold by her own master to another in North Carolina. After several months of mourning, Henry planned his escape from William Barret and Virginia.

With some assistance and inspiration, Henry decided to address a large wooden box to Philadelphia and seal himself inside to be shipped. A friend contacted the Pennsylvania Anti-Slavery Society to inform of Henry's arrival. On March 23, 1849, this large box labeled as "dry goods" was sent north by steamboat and rail. The next day, and after over twenty-four hours of confinement, the box was delivered to the society in Philadelphia where it was opened, and Henry was freed.

After this ordeal, Henry was renamed Henry Box Brown and he toured New England with copies of the Narrative of Henry Box Brown (1849), co-written by Charles Stearns. Henry would go on to write his own work, the Narrative of the Life of Henry Box Brown, Written by Himself (1851). He spent the later part of his life working as a performer and magician, which included a sizeable stint in England. He died Toronto, Canada, in 1879.

For researchers seeking to learn more about Henry Box Brown, HSP has a copy of the 1849 Narrative of Henry Box Brown (call number E 441 .A58 v.99 no.16), as well as other publications on him, such as Henry's Freedom Box (call number PZ 7 .L48 2007) and The Unboxing of Henry Brown (call number Biog E 450 .R84 2003).