[TexConfederate1861]

You misunderstood....

The casemates were the only part of the fort that has survived both Confederate & Union Bombardments.

If the Magazine HAD exploded, which it almost did, those casemates, and all in them would have been history. (no pun intended :))

[Ditto]

The point of the discussion was that when the Confederates started the bombardment of Sumter, the loss of life was not a concern. That no Union troops were killed was pure luck and had noting to do with the fortifications.

Sumter, in coordination with the other forts that encircled it on the main land, was envisioned to provide cross-fire to protect from attack from ships entering the harbor, as happened when the Union ironclades entered in 1863. But it was impossible to protect itself from attacks from the mainland. It was, in 1861, a proverbial sitting duck if any of the encircling mainland installations were in enemy hands, (which is how it eventually fell to the Union in 1864.)