Make CSS Drop Down Menu 2 Columns

Question

I currently have a CSS <ul><li> dropdown menu that uses the following code. Unfortunately I want the sub menus to display in 2 columns as there are about 16 items in that submenu. Does anyone know how to use the following code to make this drop down menu 2 columns?

.menu {
  border: none;
  border: 0px;
  margin: 0px;
  padding: 0px;
  font: 67.5% "Lucida Sans Unicode", "Bitstream Vera Sans", "Trebuchet Unicode MS", "Lucida Grande", Verdana, Helvetica, sans-serif;
  font-size: 18px;
  font-weight: bold;
}

.menu ul {
  background: #006633;
  height: 35px;
  list-style: none;
  margin: 0;
  padding: 0;
}

.menu li {
  float: left;
  padding: 0px;
}

.menu li a {
  background: #006633 url("../images/seperator.gif") bottom right no-repeat;
  color: #ffffff;
  display: block;
  font-weight: normal;
  line-height: 35px;
  margin: 0px;
  padding: 0px 25px;
  text-align: center;
  text-decoration: none;
}

.menu li a:hover,
.menu ul li:hover a {
  background: #003f20 url("../images/hover.gif") bottom center no-repeat;
  color: #FFFFFF;
  text-decoration: none;
}

.menu li ul {
  background: #006633;
  display: none;
  height: auto;
  padding: 0px;
  margin: 0px;
  border: 0px;
  position: absolute;
  width: 225px;
  z-index: 200;
  /*top:1em;
    /*left:0;*/
}

.menu li:hover ul {
  display: block;
}

.menu li li {
  background: url('../images/sub_sep.gif') bottom left no-repeat;
  display: block;
  float: none;
  margin: 0px;
  padding: 0px;
  width: 225px;
}

.menu li:hover li a {
  background: none;
}

.menu li ul a {
  display: block;
  height: 30px;
  font-size: 12px;
  font-style: normal;
  margin: 0px;
  padding: 0px 10px 0px 15px;
  text-align: left;
}

.menu li ul a:hover,
.menu li ul li:hover a {
  background: #003f20 url('../images/hover_sub.gif') center left no-repeat;
  border: 0px;
  color: #ffffff;
  text-decoration: none;
}

.menu p {
  clear: left;
}

<div class="menu">
  <ul>
    <li><a href="#" target="_self">Main Item 1</a></li>
    <li><a href="#" target="_self">Main Item 2</a>
      <ul>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
      </ul>
    </li>
    <li><a href="#" target="_self">Main Item 3</a></li>
    <li><a href="#" target="_self">Main Item 4</a></li>
    <li><a href="#" target="_self">Main Item 5</a></li>
    <li><a href="#" target="_self">Main Item 6</a>
      <ul>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
        <li><a href="#" target="_self">Test Sub Item</a></li>
      </ul>
    </li>
  </ul>
</div>

Answer 1

2018 edit

Hey, 7 years later the columns css property is well supported

ul{
  columns: 2;
}

<ul>
  <li>first item</li>
  <li>second item</li>
  <li>third item</li>
  <li>fourth item</li>
  <li>fifth item</li>
</ul>

You could probably get a similar effect with the very robust grid

---

2011 original answer

Make the ul twice as wide as the li's and float the li's left

http://www.behemothdan.com/2011/05/faux-mega-menu-in-wordpress/