Passage: According to legend, Dangun, a descendant of Heaven, established Gojoseon in 2333 BC. In 108 BC, the Han dynasty defeated Gojoseon and installed four commanderies in the northern Korean peninsula. Three of the commanderies fell or retreated westward within a few decades, but the Lelang commandery remained as a center of cultural and economic exchange with successive Chinese dynasties for four centuries. By 313, Goguryeo annexed all of the Chinese commanderies.

Question: When was Gojoseon established?
2333 BC