The Engineers at Vicksburg Part 14: Preparing for a Union crossing
Two forts connected by a covered way guarded the landing at Grand Gulf: Forts Cobun and Wade, as seen in this detail of a U.S. Geological Survey map drawn in 1864. The full map is available from the Library of Congress:

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Photo by: Mike W. Petersen |  VIRIN: 161216-A-YL201-002.JPG