The clang of bells ringing the hour echoes around the rooftops beneath my window. In the wide plain of the Valle Umbra, below the ancient walls of Assisi, domes and bell towers emerge from the morning mists. And everywhere, noisily announcing spring, the sound of birds. All this is just a 20-minute drive from Perugia airport, yet it feels as if I have travelled back centuries. Assisi is a miraculously preserved pile of stones balanced on the lower slopes of Mount Subasio in the Apennine mountain range. There are other hill towns in this part of Umbria, delightful places such as Spello and Todi where you can stumble across Renaissance masterpieces in darkened churches, but Assisi, with its secret byways and arched alleys, is special. In 1206, a local merchant’s son and failed knight called Giovanni di Pietro di Bernardone heard a call from God. He renounced his family’s wealth and took up a life of poverty, prayer and service. We know him now as Saint Francis, and it is largely due to him that Assisi, dotted with medieval and Renaissance buildings that honour his memory, is so beautiful. Eyes will be turned to the town this summer as the National Gallery in London opens what promises to be an unmissable Saint Francis exhibition featuring artists as various as Botticelli, Zurbaran and Sir Antony Gormley. Assisi is where the story begins, on Piazza del Vescovado, the spot where Francis declared his vocation before removing his fine clothes, telling his father that God was his father now and walking naked through an arch into the bishop’s palace. Archaeological digs beneath the bishop’s residence have rediscovered the arch and visitors can now walk through it, although as there are nuns about, it’s best to keep your clothes on. While Francis, freshly abstemious, gave up indulgent dining, there’s no need for you to. Slip across the square to La Locanda del Cardinale. The 16th Century exposed-brick vaulted setting is astounding but, as you enjoy barbecued monkfish and a glass of Umbrian pinot grigio, look through the glass floor to Roman mosaics and two millennia fall away. There’s more time travel next door at the Santa Maria Maggiore. Follow the steps inside the church, down through an early medieval vault and then deeper still into a Roman room decorated with murals showing dozens of bird species. And wait until you see the Roman forum buried beneath the town’s main square. Visiting it, according to the Umbria tourist board, is ‘an immersion in the bowels of Assisi’ – but don’t let that put you off, as it’s very impressive.