Vikings are required to construct or upgrade certain buildings during the course of the game as well as removing rocks.The Meade Hall is the central activity point in any Viking village. The size of your Meade Hall directly allows the number of Vikings available on Berk. It is also the place of the Berk Market where the player can purchase Fish, Wood, Runes or Card Packs. To increase your number if Viking, you must build Viking buildings. To get more Viking buildings you must upgrade the Meade Hall.
The Great Forge has a similar role to the Meade Hall. It will eventually allow you to level up your Dragons to a max level of 112. Instead of having to place new Viking buildings to get more Vikings on your island, you can upgrade your Viking Houses, Viking Shacks and Weather Vane to achieve a total of 4550 Vikings.