<p>After considering the answers to my previous question (<a href="https://stackoverflow.com/questions/252459/one-svn-repository-or-many">One SVN Repository or many?</a>), I've decided to take the 4 or so repositories I have and consolidate them into one. This of course leads to the question, <strong>what's the best way to do this?</strong></p>

<p>Is there a way to combine two or more repositories maintaining the version history for both?</p>

<p>Edit: <em>I should also point out that I'm using Assembla.com, which does not provide access to the svnadmin command, AFAIK</em></p>

<p>Another edit: <em>Does this even matter? If svnadmin works on URLs, then it's no problem then.</em></p>

Yes, using
svnadmin dump
and
svnadmin load
.
Let's assume that you have to repositories, one with HEAD revision 100 and the other with HEAD revision 150.
You dump the first repository and load it in the new one: you end up with the full story of the first repository, from revision 0 to revision 150.
Then you dump the second repository and load it in the new one: it gets loaded with its full history, the only things that change are the actual revision numbers. The history of the second repository will be represented in the new repository from revision 151 to revision 250.
The full history of both repositories is preserver, only the revision numbers change for the repository that is imported for second.
The same of course applies for more than two repositories.
EDIT: I posted while you were editing, so I didn't see your note...