It was out of season and rainy with it. Most of the tourists had gone home. We were only there because, well, we had to go somewhere and it was the nearest. We sat by a little fountain, watched a curly-haired lady walk a curly-haired dog, and I tried to Google what we were meant to be looking at only there wasn’t enough signal.

But at dinner the night before somebody was telling us about Aldous Huxley, some long story about him stopping soldiers from advancing on Sansepolcro to save the Renaissance paintings there. “He only held them back by a day,” they explained, “but it was long enough for the shape of the advanced to change.” Transpires we got a truncated version: it was Tony Clarke, an officer-turned-bookseller, who delayed the guns. Clarke remembered an essay by Huxley that described ‘The Resurrection’, by Piero della Francesca, as “the greatest picture in the world”, and lied when his commanding officer radioed him to begin firing on Sansepulcro, occupied by German troops. He said he couldn’t see any targets, the guns didn’t fire. The town was liberated by the next day and the paintings remained unscathed.

We took our time to see them; didn’t actually go to the Civic museum at all - the baby was grizzly, we hadn’t eaten, we’d have to return soon. Instead of seeing the greatest picture in the world I watched a small man luxuriate over making sandwiches for us behind a counter laden with ham.

But the frescoes in that part of the world don’t necessitate the housing of a museum. Mary, Jesus and Joseph are embedded into the walls there, protected by weathered perspex and rendered in stone. Walk along a street and you will see the glow of candles behind a heavy door, sandwiched between a pharmacy and a grocers. When we started this trip, some 18 days earlier, we started it by going into a church - M is patient, knows well by now that I can’t resist one. Dozens of chapels and altars and pews later and this is still how we’re spending our time.

I find the cathedral while M’s getting cash out. It’s telescopic, too big to understand from the outside. We have it to ourselves until an older man in good tailoring walks up the aisle with a familiar comfort and drops a coin in the tin box reading ‘OFFERTE’. There’s a click and a thud, the same as if it were a fairground attraction, but he’s just crossing himself and thinking of somebody who isn’t there.

I’m drawn in quite relentlessly by the portraits of the Madonna and child. All over Italy I’ve been looking at them, often while wearing or carrying the baby. Jesus always looks so grown-up, a little man against her chest rather than a baby. We have seen him sport ruffles and hats in Puglia, strong hairlines in Umbria. Here, in Tuscany, his face is well-defined and his curls a halo beneath a halo. He looks like a tiny full-grown human reaching for something. This one was painted 900 years ago and the faces - watchful, determined, imbued with something between reverence and fear - are still so well-defined. I look at the dull colours and think about what they must have been nearly a millennium ago, how kaleidoscopically radiant, how ethereally vivid. The blues and the golds, how people must have been dazzled after living in a world of stone and ground.

I take a bad photo on my phone and move on; the cathedral is filled with Madonnas and babies and I look at them while my own son is in the arms of his father, the two of them listening out for their voices reverberating off the high ceilings. The man making an offering has left now.

I was brought to this part of the world when I was a teenager; I carry C through the same hallways I was shown then, now. My parents showed me Madonnas too. There is one near where we are staying that Piero fella Francesca reportedly painted in a week in the 15th century. The Madonna stands flanked by two mirror-image angels, a hand on her swollen stomach, an unimpressed resilience on her face. She is haughty and beautiful beneath a flat little hat. Nearby, in the village, in the tiny museum built around the fresco - the lone surviving wall of a church after an earthquake - there is a basket. In that basket sits handwritten notes, prayers and wishes and hopes.

The baby cries and M takes him out of the cathedral, leaving me alone in this cavernous place. We move on. We eat the sandwiches. We look for baby wipes. Gradually, Sansepolcro closes for lunch.

On the way back, though, we walk through a covered street. This is the entry to the chapel where a small, clumsily translated sign tells me Piero della Francesca is buried. This is a covered street tucked into a sleeping town and the whole thing is covered in frescos. They are so faded that to navigate them is a kind of treasure hunt: a torso here, a face there, some books, an animal, a spear. We have not been to the museum. The greatest picture in the world will have to wait another day. But here, among the remnants of once-glowing paintings - egg yolk and pigment and commerce and fervour - I am both passer-by and observer among a kind of miracle. Three weeks of Madonnas and it’s among these scraps that I realise why I can’t resist them: they have survived.