The Black Gate of Mordor

The Black Gate or Morannon was a gate built across Cirith Gorgor, and the most fortified, direct entrance into Sauron's realm of Mordor.

Description
 
The Black Gate was set in an impregnable black stone and iron wall that stretched from the Mountains of Ash in the north to the Ephel Dúath in the west. The wall had but a single gate set into its length and was patrolled unceasingly, with hundreds of Orc holes on either side in which lurked thousands of Orcs ready to attack. On either side were the two Towers of the Teeth, Narchost and Carchost.

History
The Black Gate was a mighty rampart built by Sauron the Dark Lord of Mordor in the Second Age, to protect and guard the northern entrance into Mordor and to prevent invasion at the gap between the Ash Mountains and the Ephel Dúath. It was built with the power of the One Ring, like the Barad-dûr. After Sauron's fall in the War of the Last Alliance, it was garrisoned by the Men of Gondor, who raised the two great Towers of the Teeth, Narchost and Carchost, which were built on either side of the wall and were tall enough to overlook it.

 
It was backed up on the south-eastern side by the Isenmouthe, and protected by the castle of Durthang to the west; closing the passage into Mordor to evil creatures. The reconstruction of Minas Ithil, Tower of the Rising Moon, as well as the construction of the Tower of Cirith Ungol was for the same purpose.

However, Gondor's guard on Mordor eventually failed and the fortifications fell into ruin following the Great Plague and were later taken over by the servants of Sauron and were rebuilt. Once controlled by the Enemy, they became a monument of dread, evil, and awe to anyone who saw the gate. Thus the Ringwraiths and Orcs re-entered Mordor, inhabiting the abandoned fortresses and claiming them for their own uses.

During the War of the Ring, Frodo and Sam had a chance to go through the Black Gate when they arrived at Mordor, but it was so heavily fortified and guarded that they turned away and were led on a different route into Mordor by Gollum. They also saw an army of Easterlings enter the gate.

The Black Gate was the site of the last great battle of the War of the Ring. On March 25 3019, the Army of the West commanded by Aragorn Elessar and numbering some 6,000 men (plus one Elf, one Dwarf, a Wizard and one Hobbit) arrived at the Black Gate and challenged the forces of Mordor. Their intention was to draw the watchful Eye of Sauron away from Mount Doom, to allow Frodo the Ring-bearer to cast the One Ring into the Cracks of Doom and destroy it. The delay worked and the Ring was destroyed in the fires of Mount Doom, following which the Black Gate and the Towers of the Teeth immediately collapsed.