From Halopedia, the Halo wiki
Universe and lore
Catalyst is a symmetrical Arena map set in an ancient Forerunner sanctuary showing signs of being reclaimed by nature. The two teams' bases are relatively small and separated from the center of the map by compact hallways, which contrasts with the central area's long sightlines and high degree of verticality.
Catalyst was created with the intention of expanding the number of Capture the Flag maps available in Infinite, though it was also the first map that Land Grab was implemented and tested on. The Halo 3 multiplayer map Epitaph was cited as the primary inspiration for this map's architectural style.