Train was replaced by Ancient in Counter-Strike’s Active Duty map pool in 2021.
Valve made the change in May 2021, removing Train and adding Ancient to the competitive map pool. Train had long been a recognizable Counter-Strike battleground, with bombsites arranged around a rail-yard setting and train cars that created distinctive lanes, cover, and sightlines.
Ancient was introduced as a newer jungle-themed bomb-defusal map. Its addition continued Valve’s practice of rotating maps in and out of the official pool to refresh professional competition and public matchmaking.
This change is easy to mix up with later rotations. Dust II and Mirage have also moved through different competitive configurations, while Cache and Cobblestone were removed at other times. The 2021 swap specifically involved Train and Ancient.