Ernest Borgnine plays the father of Kirk Douglas. In real life he was 1-1/2 months younger than Douglas.
The three Viking ships in the film were designed using blueprints for an actual Viking ship salvaged from the water and restored by a Viking museum in Norway. It turned out that the boats built for the film were too accurate, because the modern actors were taller than their historical counterparts. Every other oar hole had to be plugged so the modern men would have room to row with a full oar stroke. Otherwise, they would hit the backs of the oarsmen seated in front of them when pushing the oar handles forward to start each new stroke.
Kirk Douglas offered all the male members of the cast a prize for the best beard, to be grown before arriving on location. All turned up with huge beards, only to find Douglas clean-shaven.
Stuntmen had practiced for weeks for the oar walking scenes. Kirk Douglas told director Richard Fleischer that he could do it and did several times. At one point when he did fall in the icy water he calmly swam over to the camera boat and asked if they had gotten good shots. He then swam back to the Viking longboat. Fleischer noted they were watching and filming an activity that had not been done in 1000 years.
Kirk Douglas was 40 when this movie was filmed in the summer of 1957, although his character was supposed to be in his 20s.