Interesting site! I think it can be converted to PHP and MySQLi database without a lot of trouble.
In this type of site, you would keep a new page for all the top menu items. ( Home, copyright, terms, etc.)
And, the data that is displayed would be dynamically loaded from the various menus. But, it will be a lot of work to set it up. Later on, this would make the site much easier for you to maintain as it grows.
Now, a few comments on how this process needs to go. Before you code anything at all, you would need to layout your plans in detail. First, you need to make a list of all your data and how you plan to index it. You need to somehow create a way to make it all easy to access in your database. This will be a long process overall as you will need to learn a lot to be able to do everything you want to. But, we are here to help you along your way. Here are some general comments on your current site and how to break it up to rewrite it in PHP and put the data into a database. These comments are to get you started thinking about the processes involved.
Your project will need three display parts. The header, content area and footer. The footer is super simple, just your copyright notice. Easy to put that into a footer.php file. The content will be the data displayed when a user selects something to read. The header section is more tricky. I should contain all the menus for all the pages. It should contain the < html> info and all of the menus all the way down to the gold horizontal menu. The gold menu will, of course, change depending on the other menus selected. One thing about the menu, I might move all the items except HOME to the footer. People who visit your site will not care about your terms/disclaimer/privacy at all. They might view them once and then never again. Therefore, you might want to make them smaller and put in the footer with your copyright notice. Just my humble opinion. And, if you do that, you can remove the home button and add some scarab beetle images next to your title to make it more fancy. On the terms/disclaimer/privacy pages, you can add a button that says “back-to-homepage” or something like that. Just my opinion.
Now, with all that said, you probably should handle the menus first. You need to list them and decide how you want them stored in your database. You have three levels of menus. First one is a title such as “Timeline”. You might want to change this so that when a user selects a sub-menu such as 8th-Dynasty, that title would be in the title area. That way, the user can see where they are at any one moment. Again, just my opinion. Next you have the real menu’s which are the year-spans. Each of these will be needed to be listed and saved in the database. And, finally, you will need the sub-menus with all the items that go under the year menus. You will need to list these and store them in your database. Once all of these are stored, you would then need to create PHP code to “populate” the various HTML code with the menus.
This brings me to another issue. You can alter the menus manually by editing the database itself, but, you might want to create an ADMIN panel that would allow you to edit them from a webpage instead of having to do it in the database manually. This would add a lot more code, but, would make your life much easier later on.
Well, then, you need to store all of your content along with links to other pages such as references and things like that. Another big step.
I have probably overstepped what you were asking for, but, wanted you to understand what you are in for. It is not as hard as it sounds. Just a different way to program a webpage. Anyone can learn this! Not hard, just a lot to learn. We are hear to help. If you need to send a private message about this, you can click on my initial “E” and click on message and send me one. But, you can just ask questions here and everyone on the site can jump and and learn with you or teach you, too. Everyone here are very helpful and you will learn a lot! Good luck and let us know when you have more questions…