City 17

Overview

The primary setting of Half-Life 2 and its episodic sequels, City 17 is a large cosmopolitan city set somewhere in Eastern Europe. Quite possibly one of the last populated cities on Earth, City 17 is the location of the Citadel, a massive, kilometers-high complex which serves as a central headquarters of the occupying armies of the trans-dimensional Combine. City 17 was once a thriving metropolis, but urban decay and Combine oppression have left the city in disrepair, and unused sections of the city are slowly being destroyed by large, mobile walls which slowly chew apart structures using heavy segmented "teeth." The city was destroyed after the events of Half Life 2: Episode 1, due to Gordon Freeman damaging the dark energy reactor in the Citadel. Following Gordon Freeman and Alyx Vance's escape from City 17, a gigantic portal storm can be seen hanging over the ruins.

Role

Before the Combine invasion known as the Seven Hour War, Gordon Freeman invaded the dimensional border world of Xen and destroyed the Nihilanth. Unknown to Gordon, the death of the Nihilanth -- who controlled the dimensional portals connecting the two universes -- caused thousands of portal storms to rage across Earth, depositing various Xen life forms, including headcrabs and antlions. More humans died from attacks by Xenian lifeforms than died in the Seven Hour War, and humanity retreated to the relative safety of its cities. Over the course of the 20 or so years between the end of Half-Life and the beginning of Half-Life 2, humanity has neared extinction, leaving most major urban centres empty. City 17 and others like it are the only habitable places left for large populations of people. This has consequently allowed the Combine to corral most humans into easily controllable areas. 
 
City 17 was unique among these remaining population centres in that it was seemingly the base of all Combine operations on Earth. During the events of Half-Life 2, City 17 is under the control of Doctor Wallace Breen, a proxy for the Combine. Order is maintained by the Civil Protection force, which regularly carries out raids on suspected pockets of resistance against combine rule. Aside from the city's human inhabitants, head crabs, barnacles and zombies roam the abandoned areas of the city and its canals.  
 
It was also the  hub of the Human resistance movement with prominent leaders such as Dr. Isaac Kleiner, Eli Vance,  and Barney Calhoun operating  in the city (both as spies and as part of a massive underground rail-road that funnelled refugees out of the city) and important locations such as Dr. Kleiner's Lab and Black Mesa East lying either within the city proper or just outside its limits.
 
Gordon Freeman's arrival in City 17 brings about a sequence of events leading up to a civilian uprising against the combine and the eventual destruction of the Citadel. Most of the populace evacuate before the entire city is then destroyed from the ensuing explosion and portal storm.

Design

City 17 borrows many design elements from Eastern European cities. It features architecture styles from pre-World War II neoclassicism, post-war classical designs, Soviet modernism, and post-Soviet contemporary designs. Due to the heavy surveillance and brutal suppression employed by Civil Protection, the city has a very Orwellian ambiance to it.   
 
Much of City 17 consists of wall-to-wall soviet-style apartment blocks, with industrial areas peppering the outskirts. Canals and a rail-road system serve as the main transportation avenues, as the combine and Civil Protection have sole use of the roads. The city is connected to other urban centres via the rail road system, although no other cities are seen in the game. The heart of City 17 is the Citadel, which dominates the skyline.
  
Viktor Antonov, the art director of Half-Life 2, grew up in Sofia, Bulgaria so it is assumed that many of City 17's design aspects are based on it.  VIktor Antonov said in the book Half-Life 2: Raising the Bar that, 

 "One of the reasons that we liked Eastern Europe as a setting was that it represents the collision of the old and the new in a way that is difficult to capture in the United States. You go over there, and you have this collision between all of these things, the new architecture, the old architecture, the fall of communism...there's a sense of this strongly-grounded historical place. We left out the Gothic themes associated with Prague and vampires and looked into a different aspect of the region."