‘Book of Ages’ by Jill Lepore

giselle potter for the boston globe

We all think we know Benjamin Franklin. He is ubiquitous and iconic, linked with the American Enlightenment, “Poor Richard’s Almanac,” electricity, early US diplomacy, and our transition from bickering colonies to nationhood.

We never figured him for much of a family man, though. As a teenager, he fled his brother’s Boston printing shop for Philadelphia. He spent years apart from his common-law wife, Deborah, while he lived and worked in London. He was estranged from his illegitimate son, William, a Loyalist during the American Revolution.

Missing from most accounts of Franklin — even from his own autobiography — is any mention of his devotion to his sister Jane, known as Jenny. In a family of 17 children, where he was the youngest son and she the youngest daughter, they grew up together.

As adults, they were rarely in the same place, but he wrote her fondly and regularly, comforted her when she grieved her many losses, and ensured her financial well-being in her final years. For her part, she adored him, doting on his letters and seeking out his other writings.

So we learn in “Book of Ages,” an astonishing, if necessarily sketchy, biography of Jane Franklin (1712-94) by Jill Lepore, a Harvard University history professor and New Yorker staff writer.

“She was, all his life, his anchor — and, in the end, his only anchor — to his past,” Lepore writes of the sibling relationship. In fact, Franklin “wrote more letters to her than he wrote to anyone.”

“Book of Ages” is the latest example of Lepore’s project of reclaiming and revising aspects of American history — a task she accomplishes, as in her 2012 essay collection “The Story of America,” with signal literary grace.

This is a work of meticulous reconstruction and high ambition. Lepore aims not just to introduce us to an interesting, overlooked figure and to round out our picture of Ben Franklin. She also wants to examine the (by now unsurprising) relationship between gaps in the historical record and gender constraints.

Reflecting Jane Franklin’s absence from the public sphere, the evidence of her life is scanty and includes not a single letter she wrote before the age of 45 (Lepore’s account of her early years is mostly inspired guesswork, based on recollections in later letters and what is known of the typical lives of the young in the period). The letters we do have — hers to her brother and his to her — survive mostly because she was Ben Franklin’s sister.

“The facts of Jane Franklin’s life are hard to come by,” Lepore writes, confessing at one point that she was so discouraged that she almost renounced the project. “Her obscurity is matched only by her brother’s fame. If he meant to be Everyman, she is everyone else.”

Lepore evokes Virginia Woolf’s invention of Judith Shakespeare, an imaginary sister to William Shakespeare, who represented the crushing effects of gender discrimination on female creativity. By contrast, Jane Franklin is not — for the most part — a product of Lepore’s imagination.

Yet she serves a similar ideological purpose. “Her education was slight, her intellect stunted, her vantage provincial, her views narrow,” Lepore writes. The contrast with her brother could not have been more stark: “He signed the Declaration of Independence, the Treaty of Paris, and the Constitution. She strained to form the letters of her name.”

Over time, as Lepore is delighted to point out, Jane started to come more into her own, departing from the strictly personal and daring to offer her brother opinions on political matters. In idiosyncratically spelled missives, she observed the colonies and Britain breaking apart and wrote to Franklin: “For my Part I wish we had Let alone strife before it was medled with . . . & followed things that make for Peace.”

While her brother traversed the Atlantic, Jane spent most of her life in their native Boston. She married at the age of 15, young even for that time. She lived modestly with a husband, Edward Mecom, seven years her senior, who was perennially in debt and perhaps something of a ne’er-do-well. We can’t really know, but Lepore doubts it was a love match: “Jane never once wrote anything about him expressing the least affection.”

No question, though, that Jane, a woman of great and mostly conventional faith, had that faith sorely tested. She loved and lost 10 of her 12 children, some in infancy and others in adulthood. A strain of instability ran in the family, and two of her sons went mad; one of the two likely survived her (along with a single daughter), but she lost track of him, as did history.

She carefully recorded each birth, death, and marriage in her family — but nothing more — in what she called her “Book of Age’s,” a slim handmade volume that gives this biography its title. Through both her personal tragedies and the stresses of the American Revolution, which forced her from her home, Jane soldiered on.

Reading and writing, gossiping and observing, she survived long enough to mourn her cherished brother’s death. “He while living was to me every enjoyment,” she wrote to his daughter, Sarah Franklin Bache. Jane Franklin herself died at the considerable age of 82. In “Book of Ages,” Lepore has lovingly resurrected her.