Not quite what I was looking for.. The block templates are already created.

What I'd like to achieve is the possibility to create a block with content which can then be referenced on multiple pages.

create a block with content which can then be referenced on multiple pages

In umbraco you have to put the content somewhere in the content tree. Creating node without a template, is a way for the content to not get an url.

A similar solution has been discussed here https://our.umbraco.com/forum/using-umbraco-and-getting-started/92091-reusable-content and here https://our.umbraco.com/forum/using-umbraco-and-getting-started/104665-how-to-do-reusable-content-global-content-for-content-editors

I would just suggest not using a macro, and use a content picker and a partial view instead.

You would need to share the templates (or copy the content) every place you display the shared content.

If you want to reuse a part of a page, say a footer, that you create on the homepage of your site, you could reference the "homepae" from any page you have, and then render the "footer" of the "homepage".

Something like this :

@{
    var homepage = Model.Content.AncestorOfSelf("homepage");
    if(homepage != null)
    {
      // partial view, that renders the footer...
      Html.RenderPartial("Footer", homepage);
    }
}