If you visit City 17, don't forget to check out the Citadel. A massive black alien structure in the center of the city, towering over the remnants of humanity, with Dr. Breen's cozy office on the top floor, Half-Life 2 begins at the foot of the Citadel and ends on its roof.

The Citadel is a tall building. So tall that even hours after you leave town, you can still see its tip buried in the clouds, pointing to the heavens. But how high is it?" Half-Life fans wanted to know.

In 2009, someone emailed Half-Life 2 writer Marc Laidlaw asking how tall the Citadel was.

Laidlaw apparently did not know either. According to the person who sent the email, Laidlaw asked a Half-Life 2 artist, who replied that it was "at least a mile" high, adding: "If anyone has an HL2 tree, load it in the model viewer and and multiply the size by 16 (since this is the skybox version) and you will get the exact height.

After various calculations, in 2012, the Citadel was finally determined to be 2,569 meters (8,430 feet) tall, or just over 1.5 miles. Very high. (Note: original calculations were even higher, nearly 3,000 meters, but were revised to account for the fact that part of the structure is underground) This is an image created for scale alongside other buildings on the planet. Recently, even the Combine Overwiki has accepted this height as correct.

However, a Redditor named Rscreamroad was not convinced and has been struggling with it for the past nine years or so, ever since the Citadel's height was calculated. He decided to recalculate it and posted the results on Reddit.

"Over the past nine years," Rscreamroad said in his post, "there have been a lot of objections that have destroyed the immersion in the game."

"I want to at least bring my ideas to the community and reopen this discussion.

Part of Rscreamroad's problem is that if the 2,569 meter height is correct, then the Citadel is only about 250 meters wide, which doesn't make much sense to anyone who has been inside the Citadel--at the end of Half-Life 2, Those of us who have explored every inch of the Citadel's interior in a combine pod know not only how tall it is, but how thin it is, and 250 meters (820 feet) is just not big enough to accommodate everything we've seen so far, from the fleet of gunships to the striders roaming around inside in a rage. It doesn't seem big enough. The track the pod rides on is quite long, suggesting that the interior is considerably larger than 250 meters wide.

So Rscreamroad did some research. He loaded the level that occurs at the top of the Citadel and looked down at the textures of the city below. In the game file, the cityscape was actually four different images, and after pasting the images together, Rscreamroad compared them to the real city and eventually discovered that the view of City 17 from the top of the Citadel was actually created from an image looking down on New York City The city was not the only one in the city. And the camera position in that photo is 8,773 meters high. Looking down from the top of the Citadel, the city is nearly 9,000 meters below.

Determining the height of the Citadel on the basis of the subsurface image may not be the most scientific conclusion. However, Rscreamroad loaded a model of the Citadel in Half-Life 2 into Blender and found that it was not that far off. He measured it in Blender and concluded that the Citadel is "27,580 feet (8,406 meters). It was also 860 meters wide and ran to 230 meters underground".

If the Rscreamroad is correct, it is considerably higher than 2,569 meters high. It is more than 5 miles high. The height of the Citadel will be about three times higher than anyone had assumed for the past decade. And being so high means that the interior will be wide enough to make riding the long combine pods more sensible.

However, Rscreamroad itself is not entirely convinced by this new measurement. In fact, there are many different versions of the Source engine (of the Citadel model). Looking at developer resources, I found information that the latest version of the engine has started using 1/12 scale for the skybox units. And in some cases, one unit is equivalent to 2/3 inch instead of 1 inch. Also, Blender itself has slightly changed its model size conversion mechanism for loaded models with versions 2.79 and 2.8+."

A 5-mile tall Citadel seems a bit too tall to me. At least the "Half-Life" community has something new to discuss; if you'd rather watch the video than read the whole Reddit post, Rscreamroad has also made a video, which can be found on YouTube.