They appear somewhere on the coast of Lithuania near big fortress that I dont remember the name.
Like ptx said , + they got some decent throwers too (I was mainly using them + mounted archers as my ranged units): I love those guys, they need to be handled with a looooot of caution but if you manage to place them nicely (no obstacles, time to throw AND retreat, no team kill...) they can one shot anything... even generals.
