One of the museum’s most arresting possessions is a drawing of each level of the Marie Séraphique, a ship that could carry up to 312 slaves.

The drawing shows that the bottom of the boat carried barrels of water while the third level carried slaves. They are shown naked, chained to the ship’s wall, seemingly not an inch of space between them.

The drawing also indicates the number and gender of the slaves acquired in Africa, how many survived the journey, and an accounting of the goods bought in the Caribbean with the earnings from the sale of slaves.

“You would not find that ship’s diagram in many other places,” said Anthony Bogues, a historian and head of the Slavery and Justice Center at Brown University, who has worked with the Nantes museum and others across Europe to rethink how they portray their slave trading and colonial past.

In the memorial, three ninth-grade girls from a school in rural Normandy stopped to read a quote on the wall from Nantes’s slave-trading heyday in the 1700s. It was from Louis Mosnier, the commander of the ship The Sun.

“23rd of March, 1774. They threw themselves into the sea, 14 black women, all together, all at the same time, in a single motion — what diligence they had, the waves were very large and rough, the winds blowing with torment. The sharks had already eaten many before it was possible to launch a boat so that we could only save seven of them of which one died.”

As one girl finished reading, she pulled her sweatshirt around her.

“It’s cold here,” she said. “I’m done.” She and the others turned to go.