Casimir I the Restorer
In his foreign policy, Yaroslav relied on a Scandinavian alliance and attempted to weaken the Byzantine influence on Kiev. In 1030, he conquered Cherven cities from the Poles followed by the construction of Sutiejsk to guard the newly acquired lands. Yaroslav concluded an alliance with Polish King Casimir I the Restorer, sealed by the latter's marriage to Yaroslav's sister, Maria. In another successful military raid the same year, he captured Tartu, Estonia and renamed it Yuryev (named after Yury, Yaroslav's patron saint) and forced the surrounding Ugandi County to pay annual tribute. According to "Heimskringla", Olaf the Swede made an alliance with Yaroslav, even though the alliance was not liked in Sweden, in order to conquer Norway.