Often the advice is to split the page & serve it in sections. You really don't have to do this.
There is a family of javascript utilities to do it for you. The important one being 'W3-include-html'
See: http://www.w3schools.com/howto/howto_html_include.asp
I use this a lot & it works fine. Just make sure that your server responds appropriately to the request.
Look closely at this and you'll find the answer: http://www.w3schools.com/lib/w3data.js
Embed the js in your page & you're sorted.
I can't give you code (I use this as a challenge for students) but I'm happy to show it working.
Cheers
Ian