MANY thousands of years ago, there were two important inventions, the wheel and the sack. As a traveler, I can’t help wondering why it took so long to put rollers on that sack to create wheeled luggage.

“It was one of my best ideas,” Bernard D. Sadow said the other day. Mr. Sadow, who was at that time a vice president at a Massachusetts company that made luggage and coats, is credited with inventing rolling luggage 40 years ago this month.

First, the background. Mr. Sadow, now 85, had his eureka moment in 1970 as he lugged two heavy suitcases through an airport while returning from a family vacation in Aruba. Waiting at customs, he said, he observed a worker effortlessly rolling a heavy machine on a wheeled skid.

“I said to my wife, ‘You know, that’s what we need for luggage,’ ” Mr. Sadow recalled. When he got back to work, he took casters off a wardrobe trunk and mounted them on a big travel suitcase. “I put a strap on the front and pulled it, and it worked,” he said.