As it happens, I have a book on airport architecture coming out shortly, so I have been living and breathing the places for a while. It's the only single building type I have so far wanted to devote a book to. And this is for two reasons. Firstly, the international airport terminal has become, strategically, the most important building type in the world. They are also landmark structures just as much as any Getty or Guggenheim museum. Secondly, they are not really buildings at all. An airport is a multi-purpose fragment of townscape that is forever wanting to join forces with the real, older, city. Airports, because they are such huge economic generators, spawn complete business districts, industrial estates, hotel enclaves, transport interchanges. Design an airport and - as those living near Stansted are now discovering - you are designing the kernel of a future town or city.

Airports have come to symbolize progress, freedom, trade, and the aspirations of their host nations on the world stage. Also noise, pollution, and fear. Airports are routinely hated and opposed by the very people who demand and use cheap flights. Not for nothing did the poet Stephen Spender, back in the early 1930s, describe the area around an airfield as "the landscape of hysteria". No wonder the novelist Rex Warner, in his 1941 allegorical novel "The Aerodrome", used the remorseless growth of a rural military airfield, which takes over an old English village, as a paradigm for the rise of Nazism.

Were Warner to write his novel today, he would find rich source material in the form of vast airports placed many miles from the cities they serve, in some cases built on artificial islands or set, like Kuala Lumpur, in tropical jungle. Such places, with their own aerial supply routes and security systems, could simultaneously withstand a siege and topple a government. This is why, in a war, the airport is always one of the first places to be seized. This is why we have seen the armed forces deployed to protect Heathrow. An airport means more than trade. It means power and constant anxiety. They are modern versions of the medieval fortified seaport, which had to handle large volumes of trade and throughput of strangers, while simultaneously defending itself from bellicose neighbours.