Wheels have been around since at least 3500 BC, when a Sumerian pictograph depicted some on a sledge. So why, I wondered as I watched the luggage tumble around the airport conveyor belt, did it take humankind nearly 5,500 years to put wheels on suitcases – and why did it take me even longer?

It was only in the late 1980s that Robert Plath, a Northwest Airlines pilot who was tired of lugging his bag around, fixed wheels and a pull-up handle to a suitcase and turned it upright. Manufacturers were sceptical, but Mr Plath sold some wheeled bags to other airline crew members and then set up a luggage company called Travelpro.