Flagship Games

Deep editorial coverage of Geoff Crammond's most consequential works: the game that invented 3D puzzle design, and the simulation series that redefined what a racing game could be.

The Sentinel box art - Firebird 1986 — The Sentinel (1986) - published by Firebird for the BBC Micro, ported to C64, Amiga, Atari ST, ZX Spectrum, Amstrad CPC, and DOS

A Game Nobody Else Would Have Built

The Sentinel (1986) is a 3D puzzle game that puts you inside 10,000 landscapes you cannot see all of at once. You are a disembodied robot. You can only look where you stand. The Sentinel, the game's antagonist, stands on the highest point of the landscape. It rotates slowly. If it sees you, it drains your energy. Your goal is to steal its position: absorb the objects around you to gain height, create new positions to teleport to, climb higher, and eventually stand where the Sentinel stands. Then you absorb it. The game was released for the BBC Micro in 1986 by Firebird. It had been made by one person.

No other game in 1986 looked like this, played like this, or thought like this. The closest analogue anyone could offer was chess - a game of information, position, and the disciplined exploitation of sight lines. The Sentinel did not have jump puzzles, combat, or a score. It had a model of vision and geometry that most games of the era - or any era - never attempted.

The Sentinel on Atari ST - a 3D polygon landscape viewed from ground level — The Sentinel (Atari ST version) - solid-filled polygon rendering on hardware from 1986. The Sentinel is visible on the peak.

Writing the Renderer from Scratch on 32K of RAM

Crammond wrote The Sentinel on the BBC Micro - a machine with 32K of RAM. He implemented solid-filled polygon rendering on this hardware from first principles. It was, by the technical assessment of the gaming press and later disassembly work, among the first home computer games to use solid-filled 3D polygons. The visual result was arresting: landscapes of grey polygonal hills that looked unlike anything else on a home computer screen in 1986.

The 10,000 levels were procedurally generated - stored as seeds, not as full level data. The game computed each landscape from its seed number. This allowed the game to contain more unique environments than could ever be stored on a floppy disk while keeping the codebase within the BBC Micro's memory constraints. Crammond wrote the Amstrad CPC conversion himself using a cross-compiler he had built; the Amiga, Atari ST, ZX Spectrum, and PC ports were handled by other developers. Steve Bak ported the Amiga and Atari ST versions; Mike Follin ported the ZX Spectrum version; Mark Roll ported the IBM PC version.

Position as the Only Resource That Matters

The Sentinel plays like a very slow, very tense game of chess where the board is three-dimensional and neither player can see it fully. You can only look where you are standing. You must create a new robot on higher ground to see further. You can only teleport to a position you can see. If you create a robot in a spot the Sentinel can see, it will absorb the robot before you can teleport to it. The game forces you to think about sightlines before you act - to model, in your head, what the Sentinel would be able to see from where it is.

Each of the 10,000 landscapes is numbered. Players who completed one landscape received a code to begin from the next. Crammond has noted that he never expected anyone to work through all 10,000. He did not program a congratulatory ending sequence because he assumed nobody would reach level 10,000.

"I never expected anyone to finish all 10,000 levels. I never put an ending in because I thought it would never be reached." - Geoff Crammond, Gamesnostalgia.com profile

How 1987 Reviewers Tried to Describe It

Contemporary press struggled to frame The Sentinel in terms their readers would understand. It was not an action game. It was not an adventure game. The Zzap!64 Gold Medal review resorted to calling it simply "unique" and noting that any attempt to place it in a genre would be misleading. The Spectrum version review in Your Sinclair noted the meditative, chess-like quality and the unusual sensation of planning moves several positions ahead in a game that offered no obvious feedback on whether a move was correct until it was too late to change.

The game appeared on multiple "best games of all time" lists in Retro Gamer magazine and similar retrospective publications. A sequel, Sentinel Returns (1998), was published by Psygnosis for PC and PlayStation. Crammond is not credited as developer on Sentinel Returns.

Still Playing It

The Sentinel remains playable today through BBC Micro, C64, and Amiga emulators. Mark Moxon's complete source code disassembly at thesentinel.bbcelite.com documents the BBC Micro original down to individual routines with explanations of how the rendering and level generation work. See Play for emulation setup instructions, and Games for platform availability details.

The Simulation That Kept Getting More Accurate

Between 1991 and 2002, Crammond released four Formula 1 racing simulations under the Grand Prix label. Each one used a genuinely simulated physics model - not approximations. Each one pushed further into the territory of what a home computer or PC could physically compute in real time. Together they represent an arc of technical achievement that has no real equivalent in gaming: a single developer, working mostly alone, advancing the state of the art in motorsport simulation across four titles and eleven years.

Formula One Grand Prix (1991): Getting the License Right

Formula One Grand Prix (F1GP) was released by MicroProse in 1991 for the Amiga, with DOS and Atari ST versions following in 1992. It was the spiritual successor to Revs, now with a full FIA license, period-accurate car liveries, and a full grid of drivers from the 1991 season. Contemporary reviews identified it immediately as the most realistic F1 game available. It was an instant commercial success on Amiga. A North American version was released as World Circuit.

Grand Prix 4 promotional cockpit image — Grand Prix 4 (2002) promotional material - the final entry in a series that began with F1GP in 1991

Grand Prix 2 (1996): Three Years Alone, One Championship Season

Grand Prix 2 was three years in development, largely by Crammond working alone. It simulated the 1994 FIA Formula 1 World Championship - a season of unusual historical significance: Michael Schumacher's first title, Ayrton Senna's fatal crash at Imola, the FIA's subsequent technical and safety overhaul. Crammond modelled the tyre compounds, the aerodynamic characteristics of the cars, the power curves of the engines, and the behaviour of the suspension under load. The game shipped for DOS only in 1996.

"Grand Prix 2 was developed almost entirely by Geoff Crammond working alone, over approximately three years. Contemporary reviews noted repeatedly that a one-man operation producing a simulation of this depth was without precedent in the genre." - Time Extension, The Making of Geoff Crammond's Formula One Grand Prix Series

Stunt Car Racer title screen - showing Crammond's earlier physics simulation work — Stunt Car Racer (1989) title screen - the physics engine Crammond developed here fed directly into his Grand Prix simulation work

What the Physics Engine Actually Did

Grand Prix 2 simulated suspension geometry, aerodynamic downforce, tyre temperatures and compound degradation, and the interaction of all of these under braking and cornering. The car would understeer if the setup was wrong, oversteer if the rear downforce was insufficient, understeer into corners from cold tyres, and behave entirely differently in the wet. No other simulation of the mid-1990s matched this depth. The AI drivers used the same physics model as the player's car.

The result was a game that was simultaneously the most accurate F1 simulation available and one of the most demanding to drive well. It was also genuinely fast-looking at the time: the 3D engine pushed polygon counts and frame rates that made the competition look primitive. See Play for how to run Grand Prix 2 under DOSBox today.

Grand Prix 3 and 4: Refinement Under Constraint

Grand Prix 3 (2000) introduced the all-new wet weather system that Crammond has identified as the game's defining technical achievement. Variable water depth across the track surface, grip changes in real time as conditions evolved, and transitions between dry and wet zones within a single lap were new to racing simulation. Some critics noted the broader game felt less polished than GP2; the weather system was universally regarded as a breakthrough.

Grand Prix 4 (2002) was the first Crammond title developed with significant external team collaboration - Infogrames' Chippenham studio contributed alongside Crammond's own Simergy studio. It simulated the 2001 season. Its MobyGames Moby Score of 8.1 placed it among the highest-rated PC simulations of the period. It was Crammond's last credited game release.

"Grand Prix 3 is the game where I made the most technical advancements, with the new wet weather system - variable water depths, grip changes as the track dried or got wetter, mixed conditions mid-race." - Geoff Crammond, Gamesnostalgia.com profile

What the Series Actually Changed

The Grand Prix series influenced every serious PC racing simulation that followed it. The genre's expectation that cars should handle based on genuine physics - that tyre temperature matters, that aerodynamic balance is a setup variable, that rain changes everything - is in part a legacy of what Crammond established in four titles across eleven years. The Modern Scene section documents the communities that still maintain and extend Grand Prix 2 and Grand Prix 4 today. A Steam re-release of all four games has been announced for 2026 in collaboration with MicroProse.