During the first decades of the 13th century he was allied with the Livonian Brothers of the Sword against Lithuanians, who looted Semigallia on several occasions.

In 1205, joint forces of semigallians and crusaders defeated Lithuanians and killed duke Žvelgaitis.

In 1225 Viestards allowed William of Modena to preach in Semigallia however he refused to accept Christianity.

In 1228 Semigallian forces under Viestards joined the Curonians in their attack against main crusader stronghold- Riga.

The Order of Viesturs (Vesthardus Rex) was founded in 1938 to commemorate the spirit of independence of the people of ancient Latvia.