Are these two sentences all worded properly?

FYI- Pax Tharkas is the fortress. During that time, and unbeknownst to Caramon, Raistlin negotiated a deal with Argat, the thane of the Dewar clan of mountain dwarves, to betray the planned defense of Pax Tharkas. The Dewar killed those manning the gates of the great fortress in the subsequent battle, causing it to fall to the invaders.