The Pit of Oblivion was a major hazard throughout the majority of Robot Wars, being introduced in the second series. Located in the bottom-left area of the arena, the pit would be used for House Robots to dispose of immobilised robots, or for other robots to push opponents in, provided it was open. When a competitor robot was either beached over the pit, or fell into it, it classed as the equivalent of a knockout.
In the reboot, the pit remained located in the bottom-left corner, however, it wasn't utilised as much due to the introduction of the Rogue House Robot and the Fog of War also occupying the same trigger as the former Pit Release Button.
The Pit of Oblivion was introduced in Series 2, being featured in the left and centre routes of the Gauntlet across the series. It was also used in two trials across the series, - Tug of War and Pinball. Following from this, the pit was used in the main arena, and was open for the duration of the match, filled with tyres. A smoke plume was produced when a robot fell in, signifying it's defeat. In Series 3, the pit was open for the first two rounds of the competition (including The First World Championship), and was closed thereafter. Sparks were also produced in this series, rather than smoke.
In the fourth series, the pit was redesigned and was a black-and-yellow striped square with a red border - an appearance that it would retain for future series. For the fourth series only, it would descend after a certain time period - roughly 100 seconds - and a siren would also be heard to announce this. However, the sound effect was added in post-production, meaning roboteers couldn't hear it. Consequently, many self-inflicted immobilisations occurred due to roboteers not noticing the open pit.
From the first series of Extreme, the pit could be opened using a pit release button (UK Series) or a pit release trigger (US Series). In Robot Wars Extreme and Series 5, the button was a yellow tyre, mounted on the wall near the pit. In Series 6, and the remainder of the international series, the pit release was a metal bumper. However, the tyre was returned in the second series of Extreme and continued as a tyre into the seventh series.
For Series 8 onwards, the pit was located in a similar location to the original arena, in the bottom left. However, the pit release tyre was in the top middle of the arena, rather than being mounted on the bottom wall near the pit, and from Series 9 onward, the odds of the pit descended were lowered, due to Rogue House Robot, and in Series 10, the Fog of War. The pit descended much quicker in the reboot and was larger than in the original arena, as it could fit up to at least eight robots, a notable example being at the end of the 10 Robot Rumble, where all defeated robots except for Terrorhurtz were pitted, either being pushed in, drove in, or were pushed in by the house robots. The interior walls were lined with lights, and warning beeps alerted roboteers to the descent. From Battle of the Stars onward, the pit emitted a mist to signify the pit had opened, rather than a plume for when they fell in. In addition, the pit descended automatically, when a defeated competitor was attacked by a house robot after 'cease' was called. In Series 10, the pit fired a plume of smoke when a robot fell in.
Plunderbird 2 drove through most of the Gauntlet, and then dove into the pit, seemingly on purpose to avoid the House Robots and secure a qualifying distance of 10.5m total. The team were mocked and called "chickens" for this behaviour.
Both machines reversed into the pit, but in The Morgue's case, it only beached itself over the pit due to its size, prompting the team to think they'd won. However, the Judges overruled this decision, and put Firestorm 2 through.
The House Robots pitted the fully mobile Wheely Big Cheese, then also pushed Wheelosaurus and Prizephita Mk2 in as well to cover this up. The judges eliminated Prizephita Mk2 despite it being the second robot pitted, as it was already partially immobile.
The House Robot yet again swung Anvil into the pit despite it having the upper hand in the battle. The judges again scored the battle up until the point of the pitting, and declared Anvil the Forces Special champion.
Chaos 2 started the battle in dominant fashion, immobilising Mastiff, but pitted itself while trying to finish its opponent off. Instead, Manta pushed Mastiff into the pit and ultimately won the battle.
With Barbaric Response and Spirit of Scorpion both immobile, X-Terminator pitted Barbaric Response to determine a winner. Regardless, the judges determined that Spirit of Scorpion had been immobilised first, and both advanced.
After the battle, Corkscrew team captain John Heatlie asked to see footage of the pit release button being pressed, as he believed the pit descended beneath Corkscrew at random. Heatlie was shown footage of Kronic 2 pressing the pit release button, and retracted his comments.
Flybot first lifted Kitty into the pit, but toppled in itself from the weight of its opponent. Cutlet then pushed Dragon onto the lip of the pit, and Gladiator knocked it in, to determine the outcome of the battle. Gladiator then pitted Cutlet for fun, and Micro-Mute drove into the pit voluntarily to escape potential damage. Finally, Refbot pitted the victorious Gladiator, and also fell into the pit itself, crushing the featherweight robots.
Mammoth became the second walker to complete a pitting in Robot Wars, after Clawed Hopper. Staglet then pitted itself after a strong performance in the battle. Sir Killalot pitted the beaten Typhoon Cadet and Mammoth to add another two robots into the pit.
Ironside3 was overturned by Pulsar's first attack, but were helped to self-right by Sir Killalot. After Sir Killalot's involvement, Ironside3 pushed Pulsar into the pit, before it went in itself. The judges ruled that Ironside3 had been immobilised after the first collision.
The most robots in the pit at once, with just Terrorhurtz being the only machine beside eventual winner Eruption not to be pitted. Expulsion, Thor and Sabretooth self-pitted, whilst Track-tion, Iron-Awe 6, Concussion and Big Nipper were pitted by opponents, and Apollo was pitted by Shunt.
Behemoth bounced off Carbide and fell into the descending pit, which had just been activated by a Nuts 2 minibot. Anthony Pritchard did not realise what had happened until the involvement of a Nuts 2 minibot was pointed out.