Partial map of Union and Confederate fortifications in Charleston Harbor during Union siege of <a href="https://en.wikipedia.org/wiki/Fort_Sumter" class="extiw" title="en:Fort Sumter">Fort Sumter</a>
Williams Engineering Co.
<ul><li><i><a rel="nofollow" class="external text" href="https://archive.org/stream/photographichist05mill#page/110/mode/1up">The Photographic History of The Civil War in Ten Volumes: Volume Five, Forts and Artillery</a></i>. The Review of Reviews Co., New York. 1911. p. 110.</li></ul>