Xaerous is the fortress of the Bacterians in Gradius. Its also home of the hive mind that has to be destroyed for peace to come on planet Gradius.
There are similar battleships(or planets) that are also home of an Bacterian leader that leads the fight.
The green fortress Vic Viper flies to is Xaerous
Appears In
Gradius (Nemesis)
Gradius II
Gradius IV
Gradius Gaiden(some of the remains appear in stage 2)
Salamander 2( some of the remains appear in stage 5)
Gradius V(Seemingly a different version; should we call it Xaerous II?)