The two Normans, it seemed, have had some interesting discussions. "It’s been full of surprises, every time I’ve gone in there," says Foster. "Norman Rosenthal comes in, and says - ‘You can’t put them that close together’. Then it’s ‘oh, you’re right, you can’t do them that far apart. But what happens if…’" Foster laughs and shakes his head. "On the one hand it drives you batty, on the other hand it’s actually very interactive."

"Sky High" is in addition to, and much bigger than, the usual little architecture room we see at the Summer Show each year. Moreover, it has been given a key position, just off the central octagon with - this year - its Eduardo Chillida rusted iron sculptures. So this is the chance for the powerful minority architecture faction at the RA to strut its stuff. It is also a foretaste of the kind of architecture shows the old lady of Piccadilly is planning, should it ever get the money to build its big new Michael Hopkins-designed extension linking it to the former Museum of Mankind behind.

There’s a lot of happenstance in this exhibition, which has been put together at breakneck speed. Its genesis was last September, when a section of the architecture Biennale in Venice was devoted to big models of fantasy towers by fashionable architects. The RA looked at those, and decided to do something more grounded in reality. Although there are some unbuilt designs here, including a few of the shortlisted entries for the World Trade Center competition and some intriguing ecological designs incorporating giant wind turbines, they are mostly real-life, the cream of the world’s crop from earliest times.