Been to both, the other on Dauphin Island.
I'm sure you remember when walking from the parking lot toward the fort, it looks like a huge mound of dirt. Once one goes through the entry, its huge!
First battlements were built by the Spaniards in the way back. (don't remember the date), but later improved on over several wars including WWII. Mobile is an important harbor with some great civil war naval battles being fought there. The phrase "damn the torpedo's, full speed ahead" was coined during a civil war battle. (torpedo's were at that time what we now use as underwater mines) When the Union breached the passage under heavy fire from the shore cannons and Southern Ships.
The entire fort is build of bricks built by hand. 22,000 black slaves were used to make the bricks and lay them during construction.
With the advent of explosive cannon shells, the brick fortifications were obsoleted quickly.
Another interesting aspect of the fort is that it was also built with defenses behind it, if it were overran and breached. There are mortar pits 200 yards behind to protect the retreating troops if that ever happened.
We took the ferry to Fort Gaines on the other side and rode it back after the tour and visiting the Alabama Aquarium.
I've posted these before, but I'll do it again to illustrate for you.
I was also reading up on the battle of Mobile Bay and learned that the phrase "damn the torpedoes, full speed ahead" may not be correct. At that time, references to the ship's speed was in the term of "X-number of bells, i.e., Four Bells, etc. Farragut was up somewhat in the rigging to better see what was transpiring and was relaying orders to someone below him to pass on to those controlling the ship.