[Pete from Shawnee Mission]

Cletus!

To "Sally Forth" means to issue from a castle gate to conduct an armed attack or raid.

From French;
saillie
projection
faire saillie: to project, to stick out
en saillie, formant saillie projecting, overhanging

https://www.france-voyage.com/tourism/guerande-500.htm

"There are many traces of medieval times in the narrow streets of Guérande, like the ramparts still present in their entirety. Classified as Historical Monuments, they allow to appreciate the centuries of history which succeeded in the city. Thus, the Porte de Saillé dates from the 12th century, while the Porte Vannetaise reveals a typical architecture of the second half of the 13th century."

The Sallie Port is a structure that Sticks out from the wall of the castle and/or overhangs the "Portway" or door.

[Cletus.D.Yokel]

Thanks.
Clear up my confusion over why the inspection gate at the Nuclear plant was called a sally-gate.