Oakland novelist Michael David Lukas fell in love with Cairo during a college semester abroad in 2000. He found the mega-city of 20 million people “humongous, vibrant, amazing, decrepit, friendly, dangerous” — but as a Jew, he was confused about his own relationship to it.

Then he chanced upon the city’s 1,000-year-old Ben Ezra Synagogue, source of the treasure trove of historical Jewish documents known as the Cairo Geniza.

“Hearing about those centuries of Jewish life in Cairo flipped a switch for me,” Lukas says in his bungalow in Oakland’s Dimond District, his terrier Rashi resting nearby. “It raised a whole lot of follow-up questions: Where are those Jews now? How could you go from this incredibly vibrant Jewish community — the center of Jewish life in the world for many centuries — to having just a dozen Jews? It made me think in a different way about Jewish history, and everything followed from that.”

By “everything,” Lukas is alluding to his new novel, “The Last Watchman of Old Cairo,” which came out in March.

Engaging and vivid, “Watchman” centers on a Muslim family that served as security guards for the Ben Ezra Synagogue for more than 1,000 years. While the synagogue and its famous geniza are real, the generations of watchmen are fictional — “ahistorical in that they never happened,” Lukas says, “but historical in that they could have happened.”

Lukas had tried writing a novel about Cairo’s Jewish community shortly after his semester there, but it didn’t work and he abandoned the project. Years later, after the 2011 publishing of his award-winning novel “The Oracle of Stamboul,” about an 8-year-old Jewish girl in the Ottoman empire, he learned of a Muslim family that had served for centuries as watchmen for a Calcutta synagogue. When he looked further, he learned of similar arrangements in Morocco and Libya.

That shifted his attempted novel about Cairo into a new realm.

“I realized this was more than a book about the Jews of Cairo,” he says. “It was a book about interconnectedness, and about how Jews interact with other communities in the city.”

As depicted in “Watchman,” those interactions are complex. The novel shifts among three different time periods: the 11th century, when a young boy named Ali becomes the first watchman; 1897, when the Jewish scholar Solomon Schechter and two British women transport the geniza documents to Cambridge University; and the present day, focusing on a young American named Yusuf who is half-Jewish and half-Muslim, and whose father was the last watchman.

While relations between the synagogue’s Jews and its watchmen are warm and respectful, they have their limits. When Ali falls in love with a Jewish girl, his romantic aspirations hit a dead end. And Yusuf’s father’s best efforts can’t prevent the looting of the synagogue during the Yom Kippur War in 1973.

“Like a lot of children of divorced parents, I’m always trying to bring people together and make peace,” Lukas says. “We [tend to think of] this binary of Jews and Arabs, but if you think about all these Jews through the centuries who were Arabs and spoke Arabic, it explodes that binary.”

The grandson of Holocaust survivors, Lukas grew up in Berkeley, attending attended Congregation Beth El and summer camp at Camp Kee Tov and Camp Tawonga. His first tantalizing taste of the Middle East came during teenage trips to Israel with the Habonim Dror youth group.

While the Muslim watchmen and their Jewish employers are the human protagonists in “Watchman,” the Cairo Geniza can also be seen as a lead player — in the same way the Sarajevo Haggadah was at the center of Geraldine Brooks’ historical novel “People of the Book.”

A geniza is a depository for sacred Hebrew texts that are no longer usable. The Cairo Geniza consists of 300,000 document fragments — everything from writings by Maimonides to lists of items in a woman’s trousseau. It’s the most important historical source on daily life in the medieval Middle East.

While playing a key role in his story, the Cairo Geniza also provided a wellspring of historical detail for Lukas to use in writing that story. His first novel had included a generous helping of fantasy amid the history. But amid today’s epidemic of “fake news,” he felt it increasingly important to stick to facts.

“I still stand by the right of fiction writers to do whatever they want,” he says. “But the postmodern idea that facts don’t matter seemed a lot more attractive in an age when information wasn’t being weaponized to destroy our democratic institutions.”

With “Watchman” complete, Lukas is beginning his next book — a novel based on the Book of Esther but set in the future. He’s also starting a new job as assistant professor of creative writing at San Francisco State University. As if that’s not enough, he and his wife, Haley Pollack, have their hands full with a new baby and a 2-year-old daughter.

How did becoming a parent affect his writing?

“First, I have a lot less time,” Lukas says. “Second, it affected the way I saw [the character] Yusuf. I’d been having trouble writing him, in part because I just saw his relationship with his parents through his eyes. Having a kid allowed me to see him through his parents’ eyes.”