How to call different aspx pages into a which is in another page

Question

How to call different aspx pages into a div which is in another page, and the references of the page is in the page which we are having div. It will look like this:

1.aspx
2.aspx
3.aspx 

Each are different pages.

default.aspx is the page where we are having:

<div>
  <pre lang="xml">
    <p>
      <a href="1.aspx" id="leftslide"> 1</a>
    </p>
    <p>
      <a href="2.aspx" id="leftslide"> 2</a
    </p>
    <div id="leftslide" align="left"> pages would load here </div>
  </pre>
</div>

Answer 1

For archieve this you can use master pages.

http://msdn.microsoft.com/en-us/library/wtxbf3hh.aspx