Nearly forgotten amid the Union victories of 1863 was the Union attempt to bring the war back to where it started: Charleston, South Carolina. The siege of Charleston became the site of numerous engineering innovations that presaged warfare of the next 60 years, as the North tried to take the city and fort that symbolized the birth of secession.
Put simply, rats tend to go where humans go, and these strange bedfellows have had a surprising impact on each other.