Editor
If you want to use the editor part of Julius, you need the files that are shipped with the original assignment editor. If you're lucky, your version of Caesar 3 already includes the editor, but if not, you can download them from the links below.
Installation
Extract the contents of the zip file for your language to the folder where your Caesar 3 installation is, and overwrite any files that are already present.
The editor does not need to be in the same language of the game: you can have a Spanish version of the game with an English editor.