The Russian explorers and raiders of the 1650s set up a number of more or less fortified camps ("ostrogs") on the Amur. Most of them were in use for only a few months and later destroyed. It is usually thought that the first such camp in the general area of today's Khabarovsk was the fortified winter camp named Achansk () or Achansky gorodok (), built by the Cossacks of Yerofey Khabarov in September 1651 after they had sailed to the area from the upper Amur. The fort was named after the local tribe whom Khabarov's people called "Achans". Already on October 8 the fort was unsuccessfully attacked by joint forces of Achans and Duchers (who had good reasons to hate the Cossacks, due to their rather heavy-handed tribute-extraction tactics), while many Russians were away fishing. In late November, Khabarov's people undertook a three-day campaign against the local chief Zhakshur (Жакшур) (whose name is also known in a more Russian version, Zaksor (Заксор)), collecting a large amount of tribute and announcing that the locals were now subjects of the Russian Czar. A similar campaign was waged later in winter against the Ducher chief Nechiga (Нечига), farther away from Achansk.