(SME)
Strongholds of Middle Earth.

In Middle-Earth, there are 7 strongholds that played an importany role in the 
tale of the One Ring. These Strongholds are Rivendell, which holds the House of
Elrond, also called The Last Homely House; Isengard, the ring of stone in Nan
Curunir (Wizard's Vale) where is the tower of Orthanc; Erebor, also called
the Lonely Mountain, containing a large Dwarven City; Dol Guldur, where Sauron
lingered in the years before his return to Mordor; Helm's Deep, the great
fortress of Rohan; Minas Tirith, the White City; Minas Morgul, the Dead City.

Rivendell is one of the last strongholds of the Noldor, the Half-elven.
It is hidden in a vale across the Fords of Bruinen, and is protectec by steep
mountainsides on one side and a river with a single bridge over it. This place
has never been defiled by evil, and no-one has ever uttered the words of Sauron
here, except Gandalf during the Council of Elrond concerning the Fate of the
One Ring.
(in the movie, he utters the Black Speech when Boromir is about to grasp the
  Ring, in the book he utters them when talking about the Test of Fire in 
  Bag End)

Isengard is the great ring of stone in the Wizard's Vale, and houses Orthanc.
Orthanc itself houses one of the 7 Palantirs, heirlooms of old Gondor and Arnor.
The ring of stone itself is utterly destroyed during the Last March of Ents 
during the War of the Ring. Orthanc was made by the Numenoreans when they where
in their height of their power and cunning. It is indestructable by any force
available in Middle-Earth.

Erebor is the Lonely Mountain that lies in the lands between Mirkwood, Dagorlad,
the Eastern Lands and the Withered Heath. It is home to the dwarves.
Deep beneath it is the burial chamber of Thorin Oakenshield. Upon the grave of
Thorin lies Orchrist, the counterpart of Glamdring. It is said that as long
as the sword lies there, the Mountain cannot be taken by force.

Dol Guldur is the fortress of Sauron in Mirkwood. Here, Thror, father of Thorin
was held captive, and Gandalf went here to investigate who or what the 
Necromancer was. Sauron retreated to Mordor when the White Council drove him
out of the fortress, letting it seem as a retreat. It was utterly destroyed at
the end of the War of the Ring by Galadriel, using the Ring of Power she had in
her caring.

Helm's Deep is the great fortress of Rohan. Here, Helm Hammerhand lies burried,
because he died when the Wold was overrun. It is said that it could not be
captured as long as men defended it. During the War of the Ring, the army of
Saruman almost managed to do so.

Minas Tirith (City of Guard) is one of the two fortress-city's that guarded 
the Capital-city of Osgiliath. When the city of Minas Ithil was captured by the
Nazgul, and was called Minas Morgul, Minas Anor became Minas Tirith. It was
besieged during the War of the Ring, and outside the walls, on the Pelennor
Fields, the decisive battle between Good and Evil was fought.

Minas Morgul (City of the Dead) was captured by the Nazgul in the period between
the Last Alliance and the end of the Third Age. It was to be razed to the ground
and purified before it would be inhabited by men again. Frodo and Sam went past
the city on their way to Mordor, being almost captured due to the One Ring's
desire to return to Sauron.

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