I've looked in the MLA handbook and at countless places online, but I can't find the answer to this.

How do I cite, in MLA format, an online full-text version of the Versailles treaty? Do I treat it as a simple web page, or as a government document, or what?

I believe as a web page.  

The author's name, date, date of publication on the site, and the web address.  I might be missing some of it, though.  It's just the format that most accurately matches that in your handbook if you have one.

ETA:  

Author(s). Name of Page. Date of Posting/Revision. Name of institution/organization affiliated with the site. Date of Access <electronic address>.

From OWL at Purdue:
http://owl.english.purdue.edu/handouts/research/r_mla.html#Electronic

Tag to top until Ma Danby gets home.  She finished her MLS a few years ago and one of her comp papers was on citing Internet sources.  She might have  some good insight.  As I recall one of the challenges of using internet cites is that they change.  So you need to potentially have more information.  Although the Treaty of Versailles can be found in a lot of places, more obscure documents might be located in only one location.  Say a letter from Tom Jefferson to John Adams might be located at the U of VA Library.    What happens if the UofVA library changes it's directory structure, sSay UVA.Library.collections.jefferson.letters.etc to UVA.edu.JeffersonLibrary.DigitalCollections.Jefferson.letters.etc somebody using your cite is screwed, it doesn't work anymore, yet the document hasn't changed and it's location is still the same.

Quoted: I believe as a web page.   The author's name, date, date of publication on the site, and the web address.  I might be missing some of it, though.  It's just the format that most accurately matches that in your handbook if you have one. ETA:   Author(s). Name of Page. Date of Posting/Revision. Name of institution/organization affiliated with the site. Date of Access <electronic address>. From OWL at Purdue: http://owl.english.purdue.edu/handouts/research/r_mla.html#Electronic

this "ETA" content is correct.