In Dota 2, the river divides the Radiant and Dire sides of the map.
The two teams begin in fortified bases positioned in opposite corners of the arena. A broad, crossable river runs diagonally through the battlefield and separates their territories, while three lanes connect the bases for much of the action. The terrain on either side includes lanes, jungle areas, neutral-creep camps, towers, and objectives.
Radiant and Dire are the modern names for the two opposing factions. They developed from the Sentinel and Scourge sides of Defense of the Ancients, the Warcraft III mod that inspired Dota 2. The river is not an impassable boundary: heroes can cross it, and bridges, ramps, movement abilities, and map paths make it part of the tactical landscape. A common mix-up is calling the dividing feature the jungle; jungles are the areas between lanes, not the central feature separating the factions.