[css] How can I get a Bootstrap column to span multiple rows?

I'm trying to figure out how to do the following grid with Bootstrap.

I'm not sure how I'd create the box (number 1) that spans two rows. The boxes are generated programmatically in the order they are laid out. Box 1 is a welcome message.

Any ideas on the best way to go with this?

Like the comments suggest, the solution is to use nested spans/rows.

<div class="container">
    <div class="row">
        <div class="span4">1</div>
        <div class="span8">
            <div class="row">
                <div class="span4">2</div>
                <div class="span4">3</div>
            </div>
            <div class="row">
                <div class="span4">4</div>
                <div class="span4">5</div>
            </div>
        </div>
    </div>
    <div class="row">
        <div class="span4">6</div>
        <div class="span4">7</div>
        <div class="span4">8</div>
    </div>
</div>

<div class="row">
  <div class="col-4 alert alert-primary">
     1
  </div>
  <div class="col-8">
    <div class="row">
      <div class="col-6 alert alert-primary">
        2
      </div>
      <div class="col-6 alert alert-primary">
        3
      </div>
      <div class="col-6 alert alert-primary">
        4
      </div>
      <div class="col-6 alert alert-primary">
        5
      </div>
    </div>
  </div>
</div>
<div class="row">
  <div class="col-4 alert alert-primary">
    6
  </div>
  <div class="col-4 alert alert-primary">
    7
  </div>
  <div class="col-4 alert alert-primary">
    8
  </div>
</div>

I believe the part regarding how to span rows has been answered thoroughly (i.e. by nesting rows), but I also ran into the issue of my nested rows not filling their container. While flexbox and negative margins are an option, a much easier solution is to use the predefined h-50 class on the row containing boxes 2, 3, 4, and 5.

Note: I am using Bootstrap-4, I just wanted to share because I ran into the same problem and found this to be a more elegant solution :)

The example below seemed to work. Just setting a height on the first element

<ul class="row">
    <li class="span4" style="height: 100px"><h1>1</h1></li>
    <li class="span4"><h1>2</h1></li>
    <li class="span4"><h1>3</h1></li>
    <li class="span4"><h1>4</h1></li>
    <li class="span4"><h1>5</h1></li>
    <li class="span4"><h1>6</h1></li>
    <li class="span4"><h1>7</h1></li>
    <li class="span4"><h1>8</h1></li>
</ul>

I can't help but thinking it's the wrong use of a row though.