Long before the human discovery of the planet the Forerunner had a presence on the planet, evidenced by the Forerunner ruins left behind. When humans reached Arcadia, unlike with a number of other planets there was no need for terraforming, the surface of Arcadia had dense jungles, vast oceans and a rich supply of natural resources. The UNSC named the six continents of the planet Avalon, Caledonia, Eire, Lemuria, Mu and Pacifica. Pirth City on Mu quickly became the largest city and soon after was classified as the capital city. Arcadia became a center of agriculture and recreation, as well as a major location for research, acting as home for the Deep Space Research Array. The settlements of Arcadia were very built up and scattered, meaning the majority of the planet was left unexplored.
In early 2531 the planet of over 3 million colonists was attacked by the Covenant and the first battle of Arcadia began. The Covenant had attacked after Arbiter Ripa 'Moramee had been directed to it by a Forerunner stellar map the Covenant discovered on the North Pole of Harvest, during the final conflict there. Under the advice of Prof. Ellen Anders and with the clearance of Admiral Preston Cole the UNSC Spirit of Fire had pursued 'Moramee to Arcadia to assist in the battle against Covenant forces. Shortly before the Spirit of Fire arrived at the planet two Covenant Battlecruisers had exited slipspace over the planet and were engaged by the UNSC ships Belfast, Texas, Pillar of Autumn and Armstrong. One of the two Battlecruisers was destroyed, while the Texas and Belfast were also destroyed, the Armstrong was venting atmosphere due to damage and the Pillar of Autumn sustained severe damage before receiving assistance from the Spirit of Fire. The surviving Covenant vessel attacked Pirth City and the efforts of the Arcadian Patrol (the police force of the planet) managed to do little to repel them. UNSC forces from the Spirit of Fire, commanded by Sgt. John Forge and including Spartan Red Team managed to hold off the Covenant forces and enable the evacuation of Pirth City, however many civilians were killed in the evacuation attempt. After the evacuation operation the Covenant managed to push the UNSC forces back to the outskirts of the city. Forge's soldiers, aided by Spartan Team Omega, managed to rally together scattered groups of UNSC troops and destroy a Covenant field base which had been posing a major threat.
The UNSC then established control of an abandoned ONI base in the Arcadian Jungle to break through a large Covenant energy shield. By strategically placing a small number of plasma-based Rhino prototypes the Spirit of Fire acquired from the Pillar of Autumn and having them simultaneously fire on the shield, they were able to break through at which point the Spirit of Fire made a number of MAC blasts on the Covenant-controlled area within. The shield was discovered to have been concealing the ruins of an ancient Forerunner temple and the construction site of a unique Scarab tank. The Scarab was larger and better armored than regular Scarabs, was equipped with a searchlight and was most likely mechanical. Although construction on the Scarab had not been completed and it was immobile, its head and plasma beam were operational. Forge's forces managed to destroy the Scarab and the UNSC diverted a considerable amount of time and energy to studying the Forerunner ruins of Arcadia, however Ripa 'Moramee kidnapped Ellen Anders from the planet to deliver her to the Prophet of Regret who wished to use her to help him take control of the Forerunner technologies of a Shield World. It was at this point that the Spirit of Fire left Arcadia to pursue the Arbiter's ship and rescue Anders.
After the first battle of Arcadia the UNSC were able to retake the planet but with its location known to the Covenant it was under major threat and so it was largely abandoned. Those who remained upon Arcadia formed the agriculture settlement of Abaskun on the continent of Mu which while self-governed and mostly lawless, provided the UNSC with much needed food supplies during the Human-Covenant war. In 2549 the Covenant attacked the planet in the second battle of Arcadia and eventually glassed it, wiping out all humanity on the planet.