The railway that stitched Italy together

In 1861, when the Kingdom of Italy declared itself into existence, it declared into existence a country that barely functioned as one. The regions that had just been stitched together, from the Alps to Sicily, spoke different dialects, ran different currencies and had spent centuries as separate states, kingdoms and republics with no particular reason to trust one another. The railway network, built out in fits and starts over the following decades, was as much a political project as an engineering one: a physical argument that Venice, Florence and Rome belonged to the same country.

It is not a coincidence that one of the new state's proudest engineering achievements was a railway through the mountains that had always kept the north and centre of Italy apart. The Apennines run like a spine down the peninsula, and the direct line between Bologna and Florence, opened in the 1930s after the original nineteenth-century route through the passes had proved slow and difficult in winter, drove tunnels through them rather than around, cutting hours from a journey that had previously meant a long detour or a hard climb. It was, at the time, among the more ambitious railway projects in Europe, and it did for the young kingdom's self-image roughly what a national road network does for any country still arguing about whether it is one: it made the distance between the regions feel like something that could simply be crossed, rather than something that defined them.

Rome itself had to be persuaded into the network almost as hard as into the kingdom. The city had spent centuries as the seat of the Papal States, governed on different priorities from the commercial north, and its rail connections lagged behind Milan's and Turin's for years after unification. When Rome was finally made the capital in 1871, the railway had to catch up with the politics rather than the other way round, which is part of why the Rome terminus, Termini, ended up being rebuilt and expanded so many times over the following century.

A route that still makes sense of the country

Ride the line from Venice to Rome today, on the fast trains that now cover it in a few hours, and the logic of that nineteenth-century argument still holds. Venice sits in its lagoon, unlike anywhere else. Bologna, an hour or so south, is a city of covered arcades and a university older than Oxford's, and it is also, unglamorously, where Italy's railways still meet and cross. Florence, reached through the tunnelled Apennines, is the Renaissance made permanent in stone, and Rome, at the end of the line, is the argument's oldest and largest piece of evidence: a city that has been the centre of something, on and off, for two and a half thousand years.

Travelling this way, rather than flying between the cities, gives the geography back its weight. You see the plain of the Po give way to the Apennine foothills, the foothills give way to Tuscany's vineyards and cypresses, and Tuscany eventually give way to the campagna around Rome, with its ruined aqueducts striding across the fields like something out of a more confident age. None of that is visible from the air, and all of it explains why the cities look and feel as different from one another as they do.

The trip, and what it can be joined to

An escorted rail journey covering Venice, Bologna, Florence and Rome does the classic route properly: enough time in each city to get beyond the headline sights, and none of the driving that would otherwise eat into the days. It is a good introduction to Italy for a first-time visitor who wants the essentials without trying to do the whole country in a fortnight, and a good refresher for anyone who has done Rome and Florence separately and never quite joined them up.

For those with more time, the same rail route can be extended south from Rome to Sorrento and the Amalfi coast, swapping the train briefly for a coach along one of Italy's most dramatic roads and adding Pompeii, Capri and the cliffside towns of the coast to the itinerary. It turns a city tour into something closer to a cross-section of the country: Roman ruins, Renaissance palaces, a lagoon city and a subtropical coastline, all reachable from the same railway that first tried to argue they were one nation.

Spring and early autumn suit the route best, before the summer heat settles properly over Rome and the Tuscan hills, and after the crowds around the Uffizi and the Colosseum have thinned a little.