THROUGHOUT THE 1840s and 1850s, Adam Plummer kept a simple diary. In a small, leather-bound book, the Maryland resident noted major life events, such as his marriage to Emily Plummer in 1841 and the births of their nine children; recorded his payments and receipts; and listed the things he owned, like a mirror and a “blue flowered suger bole.”

But Adam Plummer was a slave, and so he also wrote about events that, to a modern reader, seem far less mundane. Again and again in his diary, he struggled to detail how his family had been torn apart. On one page, he managed to write only the following in a shaky hand: “November 25 Day 1851 Emily Plummer and five Childrens who whous sold publick.”

On the next page, Plummer tried again, this time with a more even script: “Emily plummer and four Childrens on November 28, 1851 Sold at public sale. The said woman was bought by Mrs M A Thomson in the Washington City.” Since Plummer still lived on a plantation in Maryland, his wife and children were now “banished form me Eyes.”

Plummer’s diary, in short, is both a modest record of a life and something far more stark and horrifying, the notes of an American owned by someone else. It belongs to an exceptionally small body of writing: documents written by slaves while they were still enslaved. Most writing about American slavery came from freed slaves living in the North, like Frederick Douglass, or from sympathetic white authors like Harriet Beecher Stowe. But in a few cases, actual slaves wrote letters, diaries, and other private snippets for themselves—often at great personal risk.