Ferrus was a UNSC colony and mining world, very rich in metal ores.
Ferrus was first discovered in the Zeta Mu system in 2431, where it was discovered to have incredibly large amounts of raw materials. Along with its moon, Norva. The UNSC set up a small mining colony, which continued to expand as more and more workers arrived. What had once been a small basecamp was now the capital city, named Paranga (Pronounced Par-an-ger), which was the core of all mining activity on the planet. Massive docks were built to store transport ships, ready for shipping the ores offworld.
When the Human-Covenant War began in 2525, the majority of the ores were then directed to various UNSC shipyards, so they could build more warships to help fight the Covenant fleet. By 2535, the Covenant had crushed many of the outer colonies, and closed in on the inner colonies. It was decided by the Reach High Command, that defensive fleets must be stationed at each key planet, and Ferrus was one of these. Admiral Harper commanded the 63rd Defense Fleet, stationed in orbit of Ferrus. When the Covenant did find the planet in August 2536 during the Siege of Ferrus, they had only 8 ships, against the UNSC's 35. The UNSC forces destroyed all Covenant forces, except one ship which fled the battle, and they successfully saved Ferrus and its people.