"Bulwarks" would be correct, but I would put "bastions".

Here's Google's satellite view of the fortress. This enables you to see the bastions, which are so big they're difficult to appreciate in photographs taken at ground level:
https://www.google.com/maps/place/Portugal/@41.7504245,-7.46...

Wikipedia is perfectly sound on bastions:

"A bastion or bulwark is a structure projecting outward from the curtain wall of a fortification, most commonly angular in shape and positioned at the corners."
https://en.wikipedia.org/wiki/Bastion

"It has a rectangular plan, with bastions at the corners, made on the model of French Vauban construction"
https://chavesandaround.wordpress.com/2016/04/09/o-forte-de-...
(This is a dodgy translation from Portuguese but this bit is correct)

"A bastion fort or trace italienne (a phrase improperly derived from French, literally meaning Italian outline), is a fortification in a style that evolved during the early modern period of gunpowder when the cannon came to dominate the battlefield. [...]
The design of the fort is normally a pentagon or hexagon with bastions at the corners of the walls."
https://en.wikipedia.org/wiki/Bastion_fort
You can see some pictures here; although São Neutel is rectangular, the bastios are similar.