system
Given the following post, respond as if you're commenting on Reddit:
human
[LotR] How difficult would it be to capture Bara-dur?

I realized that nothing ever takes place at the great, black fortress of Mordor. We get a glimpse of the Black Gate, but do we have any details of how secure Bara-dur was? What sort of defenses it held? 

Saw an army from Gondor, composed of 60,000 men, marched from Minastirith with the intent of smashing down the Black Gate and seizing the Dark Lord's throne, what would they face? Why is everyone so afraid of Bara-dur?
gpt
Very difficult.

In the War of the Last Alliance, Sauron held out in an under siege Barad-Dur for 7 years before finally coming out in a last ditch effort.

They destroyed the tower, but the foundations were made with the power of the Ring and cannot be desteoyed while the Ring exists (though when the Ring is destroyed,  the foundations themselves also break and this is why Barad-dur is destroyed).