The Colossus (plural Colossi) is a large Protoss war machine. The Colossus stands so tall that it can be targeted as either ground or air. Its weapon has changed several times, and currently appears as a laser that quickly sweeps across a horizontal line in front of the unit, while doing damage to the entire line instantly. Ground units can move beneath Colossi.
The towering colossus is a protoss robot design dating back to the bloody conflicts of the Kalath Intercession. It strides across the battlefield on four tall, slender legs which give it an extremely high level of mobility. The great height of the machine allows it to step up and down cliffs and other steep elevations with little difficulty, and gives it a dominating field of fire.
The heavily armored hull of the colossus carries two powerful thermal lances: one mounted on each side of its body. Complex focusing and targeting systems are used to pinpoint the continuous damage output of the thermal lances for optimal efficiency. As a target is destroyed, the lances are switched to a new target instantly so that a colossus' beam cuts a fiery swathe of destruction through multiple enemies with each firing cycle.
The colossus is unusual for the fact that it was created purely as a war machine. Most protoss robots are created for industrial or resource-gathering purposes. Even the much-feared reaver is at its core a mobile manufacturing unit re-tasked to the creation of scarab drones for long-range bombardment. The mass slaughter unleashed on the kalathi by roving colossi appalled the protoss.
At the time, the Conclave outlawed the manufacture of colossi, and existing machines were deactivated before being sealed away in distant asteroids and uninhabited moons. Centuries later the war against the zerg has brought forth these engines of destruction to do battle once more.