From Richard Ellmann’s biography James Joyce:
Joyce had fixed upon June 16, 1904, as the date of Ulysses because it was the anniversary of his first walk with Nora Barnacle. He was able to obtain, perhaps on his last visit to Dublin, copies of the newspapers of that day.
In his book, Bloom’s fondest memory is of a moment of affection plighted among the rhododendrons on Howth, and so is Mrs. Bloom’s; it is with her recollection of it that the book ends. In this sense Ulysses is an epithalamium; love is its cause of motion. The spirit is liberated from its bonds through a eucharistic occasion, an occasion characterized by the joy that, even as a young man, Joyce had praised as the emotion in comedy which makes it a higher form than tragedy. Though such occasions are as rare as miracles, they are permanently sustaining; and unlike miracles, they require no divine intercession. They arise in quintessential purity from the mottled life of everyday.