They were unplanned "Five-Year Plans" for the ages: the amazing proliferation of classic novels published from 1846 to 1851 and from 1922 to 1927. And, believe it or not, one author had a book in both those periods!
I thought about those two stellar half-decades in recent weeks because many of the great novelists who wrote during those years had summer birth dates: Alexandre Dumas (July 24, 1802), Nathaniel Hawthorne (July 4, 1804), William Makepeace Thackeray (July 18, 1811), Emily Bronte (July 30, 1818), Herman Melville (Aug. 1, 1819), Marcel Proust (July 10, 1871), Theodore Dreiser (Aug. 27, 1871), and Ernest Hemingway (July 21, 1899).
By seeing those names, you can probably guess many of the books I'm about to list.
Great novels that burst on the literary scene between 1846 and 1851 included Dumas' The Count of Monte Cristo (1846), Bronte's Wuthering Heights (1847), Thackeray's Vanity Fair (1848), Hawthorne's The Scarlet Letter (1850), and Melville's Moby-Dick (1851). And then there were these mid-19th century powerhouses by authors born during non-summer seasons: Honore de Balzac's La Cousine Bette (1846), Charlotte Bronte's Jane Eyre (1847), Anne Bronte's The Tenant of Wildfell Hall (1848), and Charles Dickens' (ital)David Copperfield(ital) (1850).
(In the case of the serialized Dickens and Dumas titles mentioned, the publishing year I gave was for when the books were completed.)
The period from 1922 to 1927 saw the release of these books by summer-born authors: posthumously published installments of Proust's In Search of Lost Time (1923, etc.), Melville's posthumously published Billy Budd (1924), Dreiser's An American Tragedy (1925), and Hemingway's The Sun Also Rises (1926). Classics from that period by authors who entered the world in cooler months included James Joyce's Ulysses (1922), F. Scott Fitzgerald's The Great Gatsby (1925), Virginia Woolf's Mrs. Dalloway (1925), L.M. Montgomery's The Blue Castle (1926), Woolf's To the Lighthouse (1927), Willa Cather's Death Comes for the Archbishop (1927), and Thornton Wilder's The Bridge of San Luis Rey (1927) -- among other wonderful works.
It would take a better literary critic or historian than me to explain why so many all-time books came out during those two five-year spans. Or maybe it was just a couple of incredible 60-month coincidences. Whatever the reasons, I can't think of any other half-decade periods that produced so many classic novels.