Ladia

Amazing photo. This is not a scene from a film about Vikings. This are barges on the River Emajõgi, 19th century. Emajõgi is a river in Estonia which flows from Lake Võrtsjärv through Tartu County into Lake Peipus

Ladja was an early medieval Slavic heavy cargo ship developed in South Baltic. Norse Vikings acquired the technological knowledge to build these large vessels when Harald Bluetooth made the alliance with the Baltic Slavs, which is why we find the word in Old Norse.

Before mixing with Slavs, Norse viking ships were small, narrow and fast. Ideal for small raiding parties. Only after, when they started building wide and large "ladja" ships, were they able to cary armies including cavalry. And only then were the vikings able to transport enough troops and equipment to Britain to launch the major invasion, which culminated during Canute (Cnut the Great).

This is based on archaeological data. Source for Slavic influence on Viking ship building (and the other way round) is "A comparative analysis of early medieval shipwrecks from the southern shores of the Baltic sea" by George Indruszewski, used to work in Viking Ship Museum, Roskilde, Denmark, now at Roskilde University....