Romeo and Juliet by William Shakespeare — The reason most people have heard of Verona, though Shakespeare never visited and set the play here for reasons of romantic convention rather than local knowledge. Reading it before you arrive makes the city's tourist economy more explicable: the balcony industry, the bronze Juliet in the courtyard, the love-note walls. It also makes the play sharper — Verona's factional street violence, its summer heat, the speed at which everything happens, fits a real medieval Italian city better than a vague theatrical backdrop.
The Divine Comedy by Dante Alighieri — Dante spent years in exile at the court of Cangrande I della Scala in Verona, and dedicated the Paradiso to him. Reading the Comedy in Verona, standing in front of the Dante statue on Piazza dei Signori and the Scaliger tombs a few steps away, gives the exile's perspective a physical grounding that no classroom can replicate.
Italian Hours by Henry James — James visited Verona several times and wrote about it with the mix of aesthetic rapture and slightly superior detachment that characterises his travel writing. His chapter on Verona captures the quality of afternoon light on the Arena and the pleasure of wandering the back streets; it also belongs to a moment — the 1870s — when the city was far less visited and the sights more casually accessible.
The Stones of Venice by John Ruskin — Ruskin's great work on Venetian Gothic architecture ranges outward to include the Veneto, and his analysis of Gothic stonework and civic buildings illuminates Verona as much as Venice. The Scaliger tombs and the Duomo look different after reading his chapters on Gothic funerary sculpture.