The Alpha Centauri Asteroid Field is a section of space filled with large asteroids spanning hundreds of miles.
When Alpha Centauri was discovered and colonized, the asteroid belt was only home to a few mining installations on asteroids rich with resources and minerals by the Helghan Corporation. Once the ISA took over Vekta from the Helghan rebels, they took over the mining installations and created several more over the years. When the ISA fell back from Vekta and retreated to Gyre, they made use of the asteroid belt and turned it into a series of defenses and installations, making it a nightmare for the Helghast to break through, since they had to scan each asteroid for hidden defenses, and dig the ISA out of their military installations there. After the Helghast broke through the defensive line in the asteroid field, now deprived of resources such as metals, they did not make much use of it as most of their resources were concentrated on conquering Gyre.