You really need to see a map of the area to appreciate the engineering that went into Four Locks.
The river makes a big meander, resulting in the foot-shaped loop (Prather's Neck) you see here.
Rather than follow the rivers wandering, they decided to build a series of four locks on the top of the loop, saving a considerable amount of work in having to build a canal.
However, they short-circuited so much of the river, it required four locks in short succession to handle the change in elevation.
Lock 47 with Lock 48 in background.
Lock 49 with Lock 50 in background.
Lockhouse 48, one of the many here at this site.
The old Mule Barn, just past Lock 50.