Our insertion point is the railway terminus. We exit onto a public plaza surrounded by a jumble of architectural styles. This could be Paris or Vienna, were it not for the presence of a few ugly Communist-era buildings that indicate we have alighted somewhere in the former Eastern Bloc.
“One of the reasons we liked Eastern Europe as a setting was that it represents the collision of the old and the new” says Viktor Antonov, art director of Half-Life 2. 
In the centre of the plaza we find a video screen crudely mounted atop a stone obelisk. Our attention goes up to the broadcast playing on the screen, and then we look beyond it to a sky broken in two by a blunt mass of steel. This is the megastructure known as the Citadel, a windowless fortress ascending into cloud from the heart of the city. We stare in awe at the scale of it, standing upright like a pile driven into the surface of the planet from orbit… a collision indeed.
Ten years ago Earth was invaded and its people defeated by the extra-terrestrial forces who call themselves the Combine. The human survivors live under occupation in a few decimated cities now identified only by numbers. Playing the role of silent protagonist Gordon Freeman, theoretical physicist turned inter-dimensional freedom fighter, we have arrived in City 17 to spearhead a human insurgency against the occupying forces.
The Combine have deployed all the familiar apparatus of totalitarianism: brainwashing and doublespeak; pervasive mass surveillance; a citizenry harassed on the streets by a hostile police force and whose squalid homes are invaded by paramilitary shock troops. The city’s dilapidated pre-war buildings have had watchtowers and checkpoints grafted onto them, militarized architecture designed to intimidate. Palisades have been erected to subdivide the urban centre into cells - these mobile infestations erupt from shattered buildings, grinding obstacles to rubble as they unfurl and advance into the streets, where they deploy as multi-storey barricades.
Each palisade is a formidable mass of xeno-metallurgy that combines defensive posture with offensive threat. Buttresses end in crenelated tops; razor sharp vanes have the look of bladed weapons that could strike if we linger within reach. The effect is to create a zone of brutality that repels all but the bravest saboteur. Perturbing physicality is just one aspect of their effectiveness as weapons of psychological warfare; the other is the social and topographical dislocation caused by their mobility. Upon command they can ‘march’ to a new location and redeploy, causing unpredictable reconfigurations that invalidate maps, devour homes, and segregate neighbours, so that the ever-reshaping city becomes an unfamiliar labyrinth to its own inhabitants.
Returning to the plaza outside the railway terminus, we discover it bisected by an extra defensive growth of palisade. Inspired by our destructive antics, the citizens are in open rebellion. Combine foot soldiers are roving, ready to quell the uprising. Airborne attack units take to the sky from the innards of the Citadel, a crucial vantage point from which the invasive topography can be mapped and the occupying forces can be directed around their own mobile barricades.
We evade capture by utilising what Antonov describes as the
“hidden spaces” of City 17.
“Such secret spaces make up a lot of what you don’t see when you’re visiting a city”  – or invading it. We travel via courtyards and alleyways not surveilled by the Combine’s aerial reconnaissance and armoured patrols. Cloistered among the ancient irregular street layout of City 17’s urban centre, we discover bands of insurgents who move with impunity. Emerging from the safety of these hidden spaces into Combine controlled zones, we join skirmishes of increasing ferocity. Buildings crumble amid the chaos of artillery exchanges. In response the palisades attempt to contain the fighting, but the battle is dismantling the city too quickly for the gaps to be effectively barricaded. We scarper over the ruins and head toward the Citadel, our compass and our destination.
When finally we break through the innermost defences and approach the Combine’s fortress, we discover that its base is not built upon the foundations of the old city but instead is suspended at the centre of a gaping chasm. The landscape has been scooped away, ground and all. Standing among the debris at the ragged edge, we examine the open wound at the heart of City 17. An eerie silence is broken only by the walls of the Citadel as they groan under their own weight, and occasionally reflect the report of gunfire from the battle.
This megascale displacement is the end state of Combine occupation writ large: the total erasure of the human-made environment in favour of the Combine’s own installations. Our response is silent contemplation of the void and the act of supreme cultural violence it represents. Never has Gordon Freeman’s muteness been more appropriate to the tone of the moment.