Result

RWD対応のシンプルなタイムライン

css

スマフォ向けのコードはPen内、@media screen and (min-width: 40em)をご参照ください

.timeline {/*全体*/
  position: relative;
  overflow: auto;
}
.timeline:before {/*センターライン*/
  content: '';
  position: absolute;
  height: 100%;
  width: 5px;
  background: #dddddd;
  left: 0;
}
.timeline h2 {
  background: #dddddd;
  max-width: 6em;
  margin: 0 auto 1em;
  padding: 0.5em;
  text-align: center;
  position: relative;
  clear: both;
}
.timeline ul {
  list-style: none;
  padding: 0 0 0 1em;
  z-index: 1;
}
.timeline li {/*各コンテナ*/
  background: #dddddd;
  padding: 1em;
  margin-bottom: 1em;
  position: relative;
}
.timeline li:before {/*吹き出し*/
  content: '';
  width: 0;
  height: 0;
  border-top: 1em solid #dddddd;
  border-left: 1em solid transparent;
  position: absolute;
  left: -1em;
  top: 0;
}
.timeline h3 {
  margin-top: 0;
}
.timeline time {
  font-style: italic;
}

html

 <div class="timeline">
    <h2>2013</h2>
    
    <ul>
      <li>
        <h3>foo</h3>
        <p>hogehoge</p>
        <time>August 2013</time>
      </li>
      <li>
        <h3>bar</h3>
        <p>hugahuga</p>
        <time>July 2013</time>
      </li>
  .
  .
  .
 </ul>
</div>

via

Responsive HTML Timeline