Considering Drupal for a large (thousands of pages) hierarchical site

No 'free-floating nodes' makes it sound like you have ruled out Taxonomy, which is a common way to build a site heirarchy.

An alternative is the 'book' module, in which all content pages are arranged in a book layout - by adding sub-pages, you effectively create chapters, sub-chapters and so on, and pages can be weighted to place them exactly where required. The Drupal handbook pages are an example of a book, but I don't know how many pages it comprises. I have one site where the client has entered around 500 pages in a book so far, with no problems.

That sounds like what we need to replicate. I will investigate Taxonomy further, but certainly as far as menu navigation and the creation of new content are concerned, we use a simple folder tree structure.

One reason for this is so that URIs then take the form of a directory path - http://example.com/arts/music/performance/opera/italian - that kind of thing.

Another is to encourage authors to divide up their information into similar structures across the site, to improve usability for visitors.

One major drawback, depending on your requirements, is that book pages can only be in one place in the book, so you can't, unlike with Taxonomy, categorize content in more than one place. But for a mostly linear project for which you want a rigid structure, it might do the job.

There are plenty of occasions where the restrictions of this scheme become annoying limitations, such as when there is a good reason to have the same content in more than one place, but that isn't a change I'd be empowered to make anyway.

Oh, and don't be fooled by the very simple initial book content type - you can add CCK fields or taxonomy (for additional sorting using views, for example) to extend the basic book page into something more useful. Oh, and for further control over authoring, things like revisions (with the diff module) and workflow are very useful.

For our purposes, with over fifty web authors, absolutely essential.

My investigations so far suggest that what we require is attainable within Drupal.

We need three levels of navigation menu - global (right across the site), regional (dependent on the major subdivision) and local (dependent on the particular page).

The local menu needs to be kept to a maximum four levels deep, so its starting point will need to be reset for certain pages - again I think this is possible.

One thing I haven't yet discovered is how easy it is to replicate an important function of our current CMS - if I have a homepage for a section, and a collection of sub-pages, I need to be able to insert a link to a sub-page into the homepage, together with a teaser or introduction automatically taken from the news article. And I need the link to be updated, and the introduction to be updated, should the sub-page ever be updated or moved.

Thanks for your comments.

I will investigate further, once I've untrashed my installation (after getting a "Fatal error: Allowed memory size of x bytes exhausted" trying to install modules, although I've allocated more memory, the site including all admin pages remains completely inaccessible).