I am not sure what is going on with the URL, but I found an archive snapshot of this page, linking below:

The Conjoined Triangles of Senior-Level Development looks into how to define a senior engineer.

https://web.archive.org/web/20240223111501/https://frontside.com/blog/2016-07-07-the-conjoined-triangles-of-senior-level-development/

I can open a PR to fix this, or you could do it if you wish. let me know!