There is a small, intimate moment early on during Inside the Vatican where Gabriela the Mosaic repairman searches for a tile from the Vatican's collection of mosaic tiles.

Tasked with maintaining and restoring the monumental artworks soaring high above the marble floor of St. Peter's, the gifted artisan is forced to seek out an exact match for a small mosaic tile which has fallen away.

There are millions of pieces in the roof of the St. Peters alone and the Vatican has enough spares in store to last for at least another 500 years. The stocks Gabriela is currently using were baked hundreds of years ago.

It is a simple demonstration of how cities reach out across space and through time to sustain themselves.

Michelangelo himself pressed some of those small hard pieces of glazed ceramic into buttery mortar back in the 16th century, the most famous of thousands of artisans down through hundreds of years who have toiled constantly to maintain the Basilica.

Such grand undertakings do not come cheaply or easily of course. Fortunes to dwarf the avarice of even the greediest mortals are required to maintain that type of effort over centuries. In the Holy Roman Church the Vatican as a city is lucky to have as benefactor and overlord one of the great enduring empires of human history.

Just as the larders and the kitchens of the mini-state could draw on the produce of the farms from the countryside around Rome to feed the thousands of clerics and the tens of thousands of ordinary workers who support them, so to are the cathedrals, libraries, galleries, apartments and ancient offices of the Church  - almost all of them of them furnished with fine antique furniture, sculpture, craftwork and art – sustained by an unceasing flow of capital into the Vatican. It recalls the poem by AD Hope, 'Australia':

And for the five cities, like five teeming sores,
Each drains her; a vast parasite robber state


It has been hundreds of years since cities were able to even feed themselves, and at that point in history they were nowhere near as huge and complicated as they have since grown. A modern city cut off from its hinterland will quickly starve.

Indeed, it will collapse with much greater speed than, say, a fortified medieval town laid under siege by an enemy force. Slower in effect, but just as devastating over the medium term would be any severing of the dozens of transport and communications links modern cities enjoy with the wider world, with other cities in the hinterlands thousands of miles away.

Whether arriving in the cargo hold of a jetliner traveling at near the speed of sound, or via fibre optic cable at near the speed of light, modern cities are kept alive by unimaginable quantities of goods, services and information. They are irretrievably enmeshed in immense far-flung networks of exchange beyond the imagining of any of the Vatican's earliest inhabitants.

For the most part of course they are nowadays fixed within the borders and the power hierarchies of their host states, the Vatican included in spite of its legal status as an entity entirely separate from Rome and the Italian Republic.

Are there circumstances under which the idea of the city state might flourish again? To ask the question implies a breakdown in the current order, the collapse of the nationstate system with all of the attendant chaos and carnage.

But then in the 2000 years that the site of the Vatican has been occupied its inhabitants have seen any number of earthly powers rise and fall.

For a long time the Pope's secular rule extended up and down the Italian peninsula from their seat of power in Rome. For much of the 14th century the headquarters of the holy resided as far west as Avignon in France. At times the population of greater Rome fell away to a comparative handful of living souls including the wild goats who picked over its ruins.

The idea of cities endures while men come and go and cities themselves rise and fall. Considering dispassionately the long arc of history through which the Vatican city has endured, its probably not unreasonable to consider a future in which the world as we know it falls away but within which the city state as an idea rises again.