Archaeologists in the Houston suburb of Sugar Land are exhuming and testing the remains of 95 people believed to be African-American convicts forced to work the sugarcane fields during the Jim Crow era.

The grave sites were uncovered in April during the construction of a new school on the former site of the Imperial State Farm Prison, a notorious penitentiary named for the Imperial Sugar Company, once the nation’s leading sugar producer.

As reported in the Washington Post, officials from the Fort Bend Independent School District decided to call archaeologists to the construction site for the new building after a worker saw what looked like a human bone protruding from the dirt. The officials had been alerted to the possibility of burials by Reginald Moore, a Houston native who began researching the history of the site more than two decades ago, after working briefly as a guard at a state prison.

Now a thriving city of some 90,000 people, known for its diversity and top-notch public schools, Sugar Land was originally part of a tract of more than 97,000 acres that Mexico’s government granted to Stephen F. Austin in 1823. With Austin’s help, some 300 American families soon settled there. The first sugar plantations began operating in the 1830s, and by the 1850s the area would be an integral part of what became known as the Sugar Bowl of Texas.

During those years, African-American slaves worked to produce the sugar that gave the region its name. As Matthew Hardy wrote in Texas Monthly in 2017, picking sugar cane was even more difficult work than picking cotton. “Sugar work was about as bad as you can imagine,” historian Sean Kelley told Hardy. “People got sick, they died. Women’s fertility rates plummeted. Europeans quickly discovered that you couldn’t get people to work in this voluntarily, which is why there’s a strong historical linkage between sugar and slavery.”

After the end of the Civil War led to the emancipation of the nation’s slaves, and many of the sugar plantations in the regions went bankrupt, some plantation owners survived by leasing convicts from the state prisons. This was legal under the 13th Amendment, which had outlawed slavery and involuntary servitude, but made an exception for forced labor as punishment for a crime.

The Texas state prison population exploded after the Civil War, including a disproportionate number of black men. According to the Texas State Historical Association, from 1870 to 1912, 60 percent of prisoners in Texas were black. Inmates outsourced by Texas prisons during this period helped build the Austin Capitol Building and part of the Texas State Railroad.

In the sugarcane fields, working conditions for the convicts were abysmal due to mosquito-borne diseases, beatings and other hardships, and the plantation on the Sugar Land site became notorious in the state as the “Hellhole on the Brazos.” In the early 20th century, it was bought and incorporated into the Imperial Sugar Company. Transition to hired labor began after that, and the company owners established a company town, Sugar Land, in the hopes of attracting new workers.

After Fort Bend school district officials alerted archaeologists to the presence of burials at the construction site in Sugar Land, a team of researchers from Southern Methodist University, University of Texas and Mississippi State University began exhuming and testing the remains. Based on their results so far, they believe the graves date to between 1878 and 1910, when Texas formally ended the convict leasing program.

All of the remains the researchers have tested so far have been African-American males, except for one, which was female. They ranged in age from 14 to 70, and the archaeologists have found that many of their bones are misshapen in the same way, indicating the repetitive stress of hard labor. In addition to the remains, the researchers also uncovered rusty tools and chains the laborers might have worn.

As founder of the Texas Slave Descendants Society, Reginald Moore works to shed light on the state’s history of exploiting black labor. For him, discovery of the suspected convicts’ graves marks the culmination of a quest he has been on since the 1990s, to win recognition for the nameless former slaves and convicts who helped build Texas—and the nation.

“It was just overwhelming,” Moore told the Post of the discovery. “And then sad at the same time, because now I know these guys are here. This really did happen.”