Looks like Classical Archives has updated it's URL format for works.

Previous one:

https://www.classicalarchives.com/work/<number>.html

The current one:

https://www.classicalarchives.com/newca/#!/Work/<number>

The old URLs are being redirected to the new ones.

Example: https://www.classicalarchives.com/work/296312.html -> https://www.classicalarchives.com/newca/#!/Work/296312