Watched by border guards, machineguns at the ready, the spies would set off from either end, eyes down as they passed each other on their way to sanctuary, honour and a new life in the Soviet Union or the West. It was pure John le Carre.
Today's swaps are more mundane: spies are now an embarrassment to Moscow and Washington, and are bundled out on planes like foolish tourists without a visa. At the height of the Cold War, dozens were exchanged each year -- usually exchanged in package deals. Both East and West had a keen sense of how big a fish they had caught. If each side had a high-profile captive, a straight swap was easy.
Gary Powers, the U2 pilot shot down over Russia in 1960, was not a conventional spy, but the intelligence from his high-altitude reconnaissance was probably as valuable as the secrets sent to Moscow by the top KGB operative Rudolf Abel, arrested in the US in 1957. It was more difficult if Moscow was desperate to repatriate a key agent but had few Western assets to exchange. The Russians usually offered to throw in people picked up for breaking Soviet law in one way or another, accused of spying and held to be traded against KGB operatives.
These deals often involved three-way swaps, with spies picked up in Britain, Germany or elsewhere.
The swaps were a pragmatic way of defusing the sharper aspects of the Cold War. Sometimes they even helped East-West relations. In 1986 the Russians arrested a US Moscow correspondent, Nicholas Daniloff, whose articles angered them. He was swapped for Gennady Zakharov, a Soviet spy at the UN. As part of the deal, Reagan and Gorbachev agreed to meet at a summit in Reykjavik. Arguably that meeting was crucial in ending the Cold War.
Spies rarely enjoyed their homecoming -- those sent back to the Soviet Union were watched and followed, and missed Western luxuries on KGB expenses.