The ships were built on land, but how did men in the viking age move the ship from land into the river / sea? For example, a ship with a need of a hundred oarsmen must have been very heavy?
Please correct me if any of the statements I made in my question are wrong..
From excavations like the Weymouth mass grave, Viking longships seem to have averaged at a crew of around 50, although ships of over 100 men were not unheard of. Longships are designed to have a shallow draft, to be easily beached and refloated again to facilitate either trading or raiding, and reconstructions at the Viking Ship Museum in Roskilde have shown that the crew are sufficient to beach, refloat, and even carry the ship.