<div class="container">
  <div class="row">
    <div class="col-3">
      <div class="card">
        <div class="card-body">
          <h5 class="card-title">Special title treatment</h5>
          <p class="card-text">
            With supporting text below as a natural lead-in to additional
            content.
          </p>
          <a href="#" class="btn btn-primary">Go somewhere</a>
        </div>
      </div>
    </div>
    <div class="col-3">
      <div class="card">
        <div class="card-body">
          <h5 class="card-title">Special title treatment</h5>
          <p class="card-text">
            With supporting text below as a natural lead-in to additional
            content.
          </p>
          <a href="#" class="btn btn-primary">Go somewhere</a>
        </div>
      </div>
    </div>
    <div class="col-3">
      <div class="card">
        <div class="card-body">
          <h5 class="card-title">Special title treatment</h5>
          <p class="card-text">
            With supporting text below as a natural lead-in to additional
            content.
          </p>
          <a href="#" class="btn btn-primary">Go somewhere</a>
        </div>
      </div>
    </div>
    <div class="col-3">
      <div class="card">
        <div class="card-body">
          <h5 class="card-title">Special title treatment</h5>
          <p class="card-text">
            With supporting text below as a natural lead-in to additional
            content.
          </p>
          <a href="#" class="btn btn-primary">Go somewhere</a>
        </div>
      </div>
    </div>
    <div class="row brick">
      <div class="col-3">
        <div class="card">
          <div class="card-body">
            <h5 class="card-title">Special title treatment</h5>
            <p class="card-text">
              With supporting text below as a natural lead-in to additional
              content.
            </p>
            <a href="#" class="btn btn-primary">Go somewhere</a>
          </div>
        </div>
      </div>
      <div class="col-3">
        <div class="card">
          <div class="card-body">
            <h5 class="card-title">Special title treatment</h5>
            <p class="card-text">
              With supporting text below as a natural lead-in to additional
              content.
            </p>
            <a href="#" class="btn btn-primary">Go somewhere</a>
          </div>
        </div>
      </div>
      <div class="col-3">
        <div class="card">
          <div class="card-body">
            <h5 class="card-title">Special title treatment</h5>
            <p class="card-text">
              With supporting text below as a natural lead-in to additional
              content.
            </p>
            <a href="#" class="btn btn-primary">Go somewhere</a>
          </div>
        </div>
      </div>
    </div>
      <div class="row">
    <div class="col-3">
      <div class="card">
        <div class="card-body">
          <h5 class="card-title">Special title treatment</h5>
          <p class="card-text">
            With supporting text below as a natural lead-in to additional
            content.
          </p>
          <a href="#" class="btn btn-primary">Go somewhere</a>
        </div>
      </div>
    </div>
    <div class="col-3">
      <div class="card">
        <div class="card-body">
          <h5 class="card-title">Special title treatment</h5>
          <p class="card-text">
            With supporting text below as a natural lead-in to additional
            content.
          </p>
          <a href="#" class="btn btn-primary">Go somewhere</a>
        </div>
      </div>
    </div>
    <div class="col-3">
      <div class="card">
        <div class="card-body">
          <h5 class="card-title">Special title treatment</h5>
          <p class="card-text">
            With supporting text below as a natural lead-in to additional
            content.
          </p>
          <a href="#" class="btn btn-primary">Go somewhere</a>
        </div>
      </div>
    </div>
    <div class="col-3">
      <div class="card">
        <div class="card-body">
          <h5 class="card-title">Special title treatment</h5>
          <p class="card-text">
            With supporting text below as a natural lead-in to additional
            content.
          </p>
          <a href="#" class="btn btn-primary">Go somewhere</a>
        </div>
      </div>
    </div>
    <div class="row brick">
      <div class="col-3">
        <div class="card">
          <div class="card-body">
            <h5 class="card-title">Special title treatment</h5>
            <p class="card-text">
              With supporting text below as a natural lead-in to additional
              content.
            </p>
            <a href="#" class="btn btn-primary">Go somewhere</a>
          </div>
        </div>
      </div>
      <div class="col-3">
        <div class="card">
          <div class="card-body">
            <h5 class="card-title">Special title treatment</h5>
            <p class="card-text">
              With supporting text below as a natural lead-in to additional
              content.
            </p>
            <a href="#" class="btn btn-primary">Go somewhere</a>
          </div>
        </div>
      </div>
      <div class="col-3">
        <div class="card">
          <div class="card-body">
            <h5 class="card-title">Special title treatment</h5>
            <p class="card-text">
              With supporting text below as a natural lead-in to additional
              content.
            </p>
            <a href="#" class="btn btn-primary">Go somewhere</a>
          </div>
        </div>
      </div>
    </div>
  </div>

.card{margin:0 0 1rem;}
.row.brick{justify-content:center}