The following code shows how to layout main content before sidebars.
<!DOCTYPE html>
<html>
<head>
<link
href="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.3.1/css/bootstrap-combined.min.css"
rel="stylesheet">
<link
href="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.3.1/css/bootstrap-responsive.min.css"
rel="stylesheet">
<style type='text/css'>
.span6 {<!--from ww w. j a va2 s . c o m-->
background-color: pink;
}
</style>
</head>
<body>
<div class="container">
<div class="row">
<div class="span9">
<div class="row">
<div class="span6 pull-right">main content</div>
<div class="span3">left bar</div>
</div>
<!-- end nested row -->
</div>
<!-- end span9 -->
<div class="span3">right bar</div>
</div>
<!-- end parent row-->
</div>
<!-- end container -->
</body>
</html>