The first commercially successful rolling suitcase was invented in 1970, when Bernard D. Sadow applied for a patent that was granted in 1972 as United States patent 3,653,474 for "Rolling Luggage". The patent application cited the increase in air travel, and "baggage handling become perhaps the single biggest difficulty encountered by an air passenger", as background of the invention. Sadow's four-wheeled suitcases, pulled using a loose strap, were later surpassed in popularity by suitcases that feature two wheels and are pulled in an upright position using a long handle.