What is a mother? I thought I knew. I grew up thinking that mothers were the center of the world. Any mother, all mothers, but especially my mother. This was partly because my mother, Elizabeth Longford, made all the decisions and took every action in an extremely happy marriage that lasted 70 years. She carved the Sunday roast, she drove, she dropped us off at the schools she had chosen for me and my seven siblings to attend. My beloved father, Frank Longford, did none of these things.

That’s only half the story. The other half is the Holy Mother. As a child, I concentrated my prayers on Mary, the mother of Jesus. “Hail Mary,” I would begin, and I knew that Our Lady, the great mother, was surely listening to me in heaven. As Jesus’s caretaker from the days of the manger onward, she was the center of his family. Not St. Joseph.

I suppose it was these two beliefs, ingrained in me since childhood, that made me so shocked when I discovered that, as late as the 19th century, mothers had no legal rights whatsoever to their own children. Back then, a father had all the control and could simply take away his wife’s young children. He could move her kids far away from her and refuse to let her see or even be in touch with them.

It wasn’t until the Infant Custody Act of 1839 that mothers in the U.K. were given a legal right to take care of their own children who were under the age of seven. The law had been passed thanks to the campaigning of Caroline Norton, the subject of my newest book, The Case of the Married Woman.

I grew up thinking that mothers were the center of the world. Any mother, all mothers, but especially my mother.

I initially began to study Norton’s life for quite a different reason. I was interested in the beginnings of feminism in England, and I knew of her as a 19th-century campaigner for women’s rights there. Then I discovered what prompted her advocacy: the terrible loss of her children.

The deprivation was a result of her trial for adultery in 1836. Her husband, the Tory M.P. George Norton, had brought an adultery suit against her and the Prime Minister of England, Lord Melbourne. The evidence to prove them guilty was supplied by George Norton’s servants, who people suspect were bribed by their boss. A judge found Lord Melbourne and Caroline innocent, preventing George from divorcing Caroline. Meanwhile, George had moved their three boys—the youngest, Willie, being only four years old—to Scotland.

Caroline then unsuccessfully tried to divorce her husband, as only husbands could sue for divorce. Determined to get her kids back, Caroline decided to try to change the law. She petitioned, lobbied friends and government officials, and wrote political pamphlets in order to introduce a bill that would give mothers custody of their children. In 1839, her efforts were successful, and Parliament passed the Infant Custody Act.

The law helped mothers everywhere in England retain legal control over their children. But it didn’t help her own case. In Scotland, the law did not apply. There, George remained her sons’ sole legal guardian.

The story gets worse. While riding his pony alone one day, Willie fell off. As he died slowly from his improperly treated injuries in 1842, he called out for his absent mother. Only after Willie’s death did George finally increase Caroline’s access to her children. She looked after their schooling because George thought of teaching as a woman’s job.

Today, we have Caroline Norton to thank for ensuring that mothers have a legal stake in the lives of their children.

Antonia Fraser is the author of several books, including Mary Queen of Scots, The Wives of Henry VII, and Marie Antoinette. Her latest, The Case of the Married Woman: Caroline Norton and Her Fight for Women’s Justice, is out now from Pegasus