Reach is the closest terrestrial planet to the star Epsilon Eridani, and considered the sister planet to Earth. Reach is the forth largest planet in the Epsilon Eridani System at 15,273 kilometers in diameter, and she contains large amounts of titanium deposits which led to the mass population and militarization of the planet. Reach has two natural satellites; the large, ringed Csodaszarvas and the small, cratered Turul which was captured into Reach's orbit as recently as some 70-80 thousand years ago. The presence of these moons have created strong tidal waves, and possibly contributed to the planet's strong magnetic fields which then could have caused the strange aurora phenomenon seen throughout the blue skies.
The Forerunners maintained a presence on Reach long before human colonization. They built at least one complex beneath Menachite Mountain and left a vessel beneath the Babd Catha Ice Shelf. Both of these were later discovered and researched by the UNSC, specifically the Office of Naval Intelligence from CASTLE Base. Archeological evidence suggests that the vessel was outbound from the complex beneath the mountain, and it left behind a trail of debris before crashing.
Insurrectionist activity has on more than one occasion spread this planet. Rebels planted explosives and targeted hotspots in hopes of crippling the Achilles Heel. The legendary SPARTAN-II super soldiers were trained on Reach at the Reach FLEETCOM Military Complex. In 2552, a Covenant task force arrived at Reach with the intentions of uncovering the abundance of sacred Forerunner relics before the main fleet arrives.
Having been denied their claim on the Forerunner relics because of NOBLE Team, the Covenant task force proceeded to make a final assault. NOBLE Team develops one last plan, Operation: UPPERCUT, to capture a Corvette and rig it with a makeshift Slipspace Bomb heading straight for the Supercarrier Long Night of Solace. This operation is a success, but it comes at the cost of Jorge-052's life. A significantly larger Covenant fleet arrived on August 14 and began to lay siege on several cities on the planet. The final battle for the planet was fought when a massive Covenant invasion fleet over 300 ships strong arrived in the morning of August 30.
The majority of the SPARTAN-IIs aboard the Pillar of Autumn were dispatched to the planet's surface to protect the generators for the orbital defense platforms, while a small team led by John-117 boarded Reach Station Gamma to secure an unprotected NAV database aboard the ONI prowler Circumference. Eventually, the Autumn was one of the few ships to escape the battle. The conflict led to catastrophic casualties on both sides, and resulted in the glassing of most of Reach's surface save for CASTLE Base which stood over a Forerunner complex. The Covenant sought to gain access to this complex, but were beaten by a team of Spartan-IIs who recovered the treasured Forerunner crystal and left the system.
In November 2553, a pioneer group arrived on Reach for an initial search and preparation for the planet's reterraforming. BXR Mining Corporation restored their facilities and established a makeshift settlement known as Cooper Station.