Roberto Calasso, an Italian writer who became known as one of his country’s foremost modern intellectuals, leading an influential publishing house for decades and exploring themes from Greek mythology to Kafka in his own works of dazzling erudition, died July 28 in Milan. He was 80.

Francesca Marson, a spokeswoman for Adelphi Edizioni, where Mr. Calasso had long presided as editorial and managing director, confirmed his death but did not cite a cause.

Mr. Calasso — once described by the Paris Review as “a literary institution of one” — was the author of a shelf full of books that contained a breadth of subject matter great enough to fill a library.

He was perhaps best known for his book “The Marriage of Cadmus and Harmony,” a retelling of Greek mythology first published in Italy in 1988. But his works also touched on Vedic India, the 18th-century Italian painter Tiepolo, the French turncoat Talleyrand and the writings of authors from Baudelaire to Karl Marx. Sprawling but not scattered, his oeuvre was connected by a ceaseless search for understanding of civilization and the stories that sustained it — mythological, historical and philosophical.

“Stories are the most durable texture of life for us,” Mr. Calasso once told the London Independent. “Not forms of societies, but stories. Stories are really what keeps everything together, in a way. When you are abandoned by stories — when you go back beyond the invention of writing, beyond the literary tradition — you feel of course lost: because one needs stories.”

To the casual observer, Mr. Calasso might have seemed the quintessential austere European intellectual. But his writing and imagination were vivid enough to attract impressive numbers of readers. “The Marriage of Cadmus and Harmony,” which was translated into English by Tim Parks, reportedly sold more than 200,000 copies in Italy alone.

“Like Ovid, Mr. Calasso has a distinct authorial presence,” Mary Lefkowitz, a scholar of Greek myth, wrote in the New York Times, comparing Mr. Calasso to one of the most celebrated poets of antiquity.

“He offers judgment on both characters and stories, and on their relationship to the modern world,” she continued. “But where Ovid treats his characters with mild condescension and some irony, Mr. Calasso treats them with the kind of respect believing pagan writers like Homer and Callimachus might have given them. Also unlike Ovid, Mr. Calasso often provides several different versions of a story, so that his readers can see the various potential meanings a myth can have.”

Mr. Calasso was said to have taken pride in the words of another reviewer, the Italian novelist and intellectual Italo Calvino, who wrote admiringly of Mr. Calasso’s book “The Ruin of Kasch.” In that work, published in Italy in 1983, Mr. Calasso departed from the French Revolution in a march through history so long, Calvino reputedly quipped, that the book could be said to have two topics: “The first is Talleyrand; the second is everything else.”

“In just under 400 pages, Mr. Calasso manages to quote Goethe, Sainte-Beuve, the Upanishads, Frazer’s ‘Golden Bough,’ ‘Das Kapital,’ the German anthropologist Leo Frobenius . . . and several hundred other works in several languages,” the literary biographer James Atlas wrote in the Times. “His model, the German critic Walter Benjamin, aspired to write a book that would consist of nothing but quotations; Mr. Calasso has very nearly done just that.”

Mr. Calasso conceded to Atlas that “The Ruin of Kasch” was “a bit like a forest, where you lose yourself.” But to admirers who marveled at the density of the forest Mr. Calasso had conjured, making one’s way through the woods was both the challenge and the pleasure of braving his works.

Mr. Calasso’s other books included “The Impure Fool,” based on a famous patient of psychoanalyst Sigmund Freud; “K.,” a rereading of the works of Franz Kafka; “Tiepolo Pink,” about the artist regarded as a master of the technique called sprezzatura; and “The Celestial Hunter” about, in part, the history of hunting in Western civilization.

Mr. Calasso traced his love of literature to his childhood in Florence, where he was born on May 30, 1941. His maternal grandfather, a philosophy professor, founded a publishing house, La Nuova Italia. Mr. Calasso’s mother was a literary scholar, and his father was a professor of the history of law.

“He used to work on texts mainly from the 16th to 18th century, so the house was full of marvelous folios,” the London Observer quoted Mr. Calasso as saying. “I grew up surrounded by old books. I was always in the midst of books.”

Mr. Calasso said he began writing his memoirs at about the age of 12. By all accounts, he had already accumulated ample experience to fill them. During World War II, his father, an anti-fascist, had been arrested and condemned to death in what Mr. Calasso described as a reprisal for the assassination of the fascist philosopher Giovanni Gentile. The father was ultimately freed, but the family had to go into hiding, with the young Mr. Calasso learning to use an assumed name.

At 21, after studying at the University of Rome, Mr. Calasso was hired by Adelphi Edizioni, where he eventually became majority owner. Adelphi has published the works of such writers as Jorge Luis Borges and Milan Kundera, earning a reputation in Europe and beyond as a house that valued ideas over profits.

In a tribute to Mr. Calasso published in the Italian daily the Corriere della Sera, the physicist Carlo Rovelli, author of the best-selling “Seven Brief Lessons on Physics,” recalled an early conversation with Mr. Calasso.

“Carlo,” Mr. Calasso said, “I’ve read what you wrote. I like it. Whatever you write that you consider important, send it to me. Don’t worry about writing books that will sell. Think only about the true things you have to say. I will publish them for you.”

Mr. Calasso’s survivors include his wife, the Swiss writer Fleur Jaeggy; two children, Josephine Calasso and Tancredi Calasso, both from an earlier relationship with the German writer Anna Katharina Fröhlich; several siblings; and several grandchildren.

Mr. Calasso drew a distinction between information and knowledge, the first being something that one searches for and locates, and the second being something that must be cultivated over a lifetime. It was a difference, he observed, that was often forgotten in the digital age, when facts and figures but not necessarily understanding are a few clicks away.

“The word ‘information’ suffers from a kind of verbal inflation, which has confused the minds of lots of people,” he remarked in 2015. “And that is really worrying. Not the simple fact of digitization, which I’m not scared of, but that in the mind of some people, these two terms conflate. But they are opposites, sometimes.”