evidence: Noktundo (Korean: 록둔도/녹둔도) was an island in the delta of the Tumen River on the border between Primorsky Krai, Russia and North Korea.[1] The area of the island was 32 square kilometres (12 sq mi).[2][3] Noktundo had been Korean territory since the 15th century.[3] The Jurchens took notice of this. In 1587 there was a battle fought on this island between the local Koreans and the invading Jurchens from nearby Russia. At first, the Jurchens successfully sacked the island and captured 160 Koreans as prisoners. As they crossed the river back to their camp with the prisoners, the famed Korean general Yi Sun-Shin, chased after the invaders and rescued 50 Koreans and defended the island. With his army, he later infiltrated the nearby Jurchen army camp, and captured their leader alive.[4]