Technological Achievement Tiers

The Forerunners categorized the Technological Advancement of civilizations into Tiers. This system was later adopted by the Covenant. All life and civilizations fall into one of the categories. The lower the Tier number, the more advanced the civilization is/was. It should be noted that this is a reference to bungie's number 7

Tier 7: Preindustrial
Tier 7 is one of the most common and stable states, with limited weaponry and environmental threats. Societies tend to be small and scattered, driven by subsistence farming, foraging, or hunter-gathering needs. Technology is limited to simple tools, weapons, or agrarian implements and methods, but a basic understanding of planetary and solar mechanics is not uncommon.

Tier 6: Industrial Age
Tier 6 is often the pinnacle for a civilization. Agrarian societies can remain stable in the preindustrial stage, but Tier 6 population strain and mechanized food production invariably create political and economic pressures few can balance. Moving past this usually promises advancement. Some societies improve environmental and medical understanding concurrently with mechanical and transport advancement; those that do not are frequently doomed.

Tier 5: Atomic Age
Tier 5 species usually become space-farers, focusing on clean energy production. The occasional belligerent species will use atomic energy for weapons, often resulting in extinction. In-atmosphere craft are a hallmark, often leading to spaceflight.

Tier 4: Space Age
Tier 4 is often the final resting place for species intelligent enough to break free from their cradle's surface only to fill the gulf surrounding it with war. Their comfort-focused technology can include medical advances. 21st Century (Present Day) Humanity stands at this level.

(Note: Jiralhanae (Brutes) are the only species on record who achieved space, reduced themselves through internecine (civil) war to a preindustrial condition, clawed their way back to their former state and learned nothing from the experience.)

Tier 3: Space-Faring
Humans have efficient Slipspace navigation, mass drivers, asynchronous linear-induction weapons, holocrystal storage and semi-sentient AI (though their creation requires memory transfer from freshly deceased and/or flash cloning). They have had no outside influence - until recent events. Since Covenant contact, they have been on the verge of huge artificial advancement. 26th Century Humanity stands at this level.

Tier 2: Interstellar
The Covenant's ability to perform accurate slipspace navigation, near-instantaneous communication and man-portable application of energy manipulation owes itself to Forerunner technology. The unified state of the 26th Century Covenant stands at this level. The Sangheili are also at this level.

(Note: The two primary extant interstellar civilizations were space-faring prior to discovering Forerunner artifacts - or each other - but they have not successfully reverse-engineered those artifacts.)

Tier 1: World Builders
The Forerunners ability to manipulate gravitational forces, create AI with full sentience, fabricate super-dense materials, perform ultra-accurate slipspace navigation and the ability to create worlds (e.g.; Onyx, the Halos and the Ark) is unequaled by any existent civilization.

Tier 0: Trans-sentient
As the Forerunners had no examples of civilizations with technological accomplishment greater than themselves - with the exception of the Precursors - this is a theoretical ceiling. They can travel intergalactic and accelerate the evolution of intelligent life.