The Great Northern Expedition (Russian: Великая Северная экспедиция) or Second Kamchatka Expedition (Russian: Вторая Камчатская экспедиция) was one of the largest exploration enterprises in history, mapping most of the Arctic coast of Siberia and some parts of the North American coastline, greatly reducing "white areas" on maps. It was conceived by Russian Emperor Peter the Great, but implemented by Russian Empresses Anna and Elizabeth. The main organiser and leader of the expedition was Vitus Bering, who earlier had been commissioned by Peter I to lead the First Kamchatka Expedition (1725 to 1731). The Second Kamchatka Expedition lasted roughly from 1733 to 1743 and later was called the Great Northern Expedition due to the immense scale of its achievements.