Architecture of the World Wide Web, Volume One will be soon 20 years old. ❤️ Published on 15 December 2004.
https://www.w3.org/TR/webarch/
If you have never read it, I encourage you to do it. It's a milestone.
Things have changed a lot since its publication, and if you want to understand what the Technical Architecture Group (TAG) is up to these days, be sure to follow what is happening on the TAG homepage. https://www.w3.org/2001/tag/