Thread:User talk:CodeCat/Why did you remove the Sexagenary cycle category I created?/reply

The category structure is stored in a number of modules, Module:category tree/topic cat and its subpages. This is done so that all languages can easily share the same tree structure and there is no redundant information. If you add categories manually then it bypasses that whole system.

Also I wonder why you created the categories if they show errors like that.