 Later that year , in August , he captured Velizh in September he participated in the siege of Velikiye Luki , and then took Zavoloc . On 11 August 1581 he received the nomination for the post of Grand Crown Hetman ; this nomination , although uncontroversial at that time , was technically illegal . Following that he participated in the long and inconclusive Siege of Pskov , which ended with the Peace of Yam @-@ Zapolsky in 1582 . Though Zamoyski failed to capture Pskov , he drained the Russian resources , and the ongoing siege was a major reason for the final treaty , which was highly favorable to Poland . 
