There is no need, in my opinion.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
AnonymousBy destroying Gunthar’s intelligence network, Kitiara ensured that the flying citadel (that) she possessed would remain a secret for as long as possible.I would prefer leaving leaving it out. Not that it is wrong grammartically. It just sounds more smooth. Another thought: