How to have the same html on all webpages without having to update the pages individually?

I'm making a yahoo geocities webpage, and I want to have a navigation bar at the bottom of every page. I've written the html for it, but is there a way, like inserting a css stylesheet, that I can insert the navigation bar onto all the pages without typing out the full code? So that when I make a new page that needs to go in the navigation bar, I don't have to edit every single page with it on.

How to have the same html on all webpages without having to update the pages individually?
Unfortunatley Yahoo hasn't begun that process, but building a page one at a time is better I think.
Reply:I don't know if geocities allows for server side scripting like PHP or ASP .NET, but this is how you would do it if you were able to use this language. However, if you can only use HTML, I'm afraid your stuck doing it the long and boring way of 'copy and paste' into every HTML file.
Reply:Edit your shared borders. The shared borders, Top, left, and bottom are displayed on all pages.