In a passage that overflows with visual and olfactory imagery, the narrator uses oxymoron to describe the setting:
A few days after his brief interview with her mother, he encountered her in that beautiful abode of flowering desolation known as the Palace of the Cæsar. [...] He stood looking off at the enchanting harmony of line and color that remotely encircles the city, inhaling the softly humid odors, and feeling the freshness of the year and the antiquity of the place reaffirm themselves in mysterious interfusion.
The oxymoron "flowering desolation" captures the gloom that at times accompanies excess. The palace may be full of blossoms, but it is ultimately a relic of the ancient past. This contrast makes Winterbourne feel as though he is surrounded by life and death all at once. Spending the peak of Spring among the ruins of a bygone era leaves him feeling torn. For Winterbourne, who is ultimately an outsider in Rome, the Palace of the Ceasar is both inviting and inhospitable.
Later in the passage, the narrator comments on how, in Spring, the city is simultaneously fresh and ancient. This blends together in a "mysterious interfusion." These two sets of discordant qualities provide insight into Winterbourne's inner experience at this point in the narrative. Although he continues to feel drawn to Daisy, he nevertheless begins to feel worn out by his frustrating, ambiguous pursuit of her. He is unsure of what he wants out of their relationship and unsure of what he's doing in Rome.
The desolation lurking beneath the flowering prime of the setting hints at Daisy's coming death. This is one of the final times he sees her in full health and vigor. Struck by the complementary beauty of Daisy and the setting, he is left feeling melancholy. Similarly, the ancient atmosphere in Rome reminds Winterbourne of all the people who have passed through the eternal city and subsequently been survived by it. Staring out across Rome seems to remind him of his mortality; he recognizes that his little life is nothing when compared with its enduring vitality.
