A rare photo, released by the White House, shows Barack Obama fielding calls from a tent in Brazil, to keep up with events in Libya. The tent is a mobile secure area known as a Sensitive Compartmented Information Facility, designed to allow officials to have top secret discussions on the move.

They are one of the safest places in the world to have a conversation.

Designed to withstand eavesdropping, phone tapping and computer hacking, Sensitive Compartmented Information Facilities - also known as SCIFs - are protected areas where classified conversations can be held.

The problem with writing a biography of Socrates, as Bettany Hughes merrily admits, is that he’s a “doughnut subject”: a rich and tasty topic with a big hole right in the middle where the main character should be. Despite his fame and his insistence on an examined life, Socrates never wrote anything, and our knowledge of him comes mainly from three contemporaries — his devoted pupils Plato and Xenophon, and the parodist Aristophanes — each of whom had his own agenda. He produced no great answers, only great questions, and the most enduring image we have of his life is his leaving of it, as the title of this book suggests.