This page contains a few packages that contain map data for the Qt version of Marble. You can install this data manually. Users of the KDE version can get these maps with Download maps... in the File menu You have to extract these files into Marble's maps directory. On Windows this is data/maps in your Marble installation. On Linux you will find it in $XDG_DATA_HOME/marble/maps while $XDG_DATA_HOME is usually ~/.local/share.
Here's an example for Linux and the Historical Map 1570: Download the map theme using the download link in the table below, saving the file as ortelius1570-marblemap.zip. Open a shell and run
unzip -d ~/.local/share/marble/maps ortelius1570-marblemap.zip
Now you just need to run Marble and select the newly installed map theme.