Fortress

There are many fortresses and strongholds in Arda, such as Minas Tirith, Helm's Deep, Minas Morgul, and Barad-dûr.

Overview
Fortresses and keeps are military constructions which have buildings built for warfare and defense and are generally fortified. The defensive positions act as command headquarters and sometimes capitals of realms. Some fortresses are just simple walled-in villages, such as the town Bree. Positions fortified like Bree with only a stockade would not hold back a major assault. Many other fortresses were heavily defended with strong, well-constructed stone keeps, such as the Hornburg in Helm's Deep. The most powerful fortress of men in Middle-earth was Minas Tirith. It was built on a hill below Mount Mindolluin. It had 7 levels, each surrounded by a ring of walls 100 feet high. At the top of the 7th level there was a tower 300 feet high, 1,000 feet above the plain, giving a commanding view of the Pelenor. Other than the extremely strong Gate of Minas Tirith on the first level, each gate to the next level was staggered, so that an enemy would have to conquer the whole level before advancing. This also gave the defenders time to retreat and regroup on the next level. Minas Tirith was also defended by a battery of 100 trebuchets (large, counterweighted catapaults) on its walls, which could launch boulders onto the plain below.

Fortresses/Strongholds of Men

 * Minas Anor (later called Minas Tirith)
 * Osgiliath
 * Minas Ithil (later Minas Morgul after being captured by Sauron)
 * Isengard (with the tower of Orthanc within)(later used by Saruman for evil purposes)
 * Durthang (later captured by Sauron)
 * Tharbad
 * Fornost
 * Amon Sul (ruined in the Third Age)
 * Helm's Deep (with the Hornburg within)
 * Edoras
 * Dunharrow
 * Aldburg
 * Umbar (later taken by the Corsairs)
 * Bree

Fortresses/Strongholds of Elves

 * Caras Galadhon (the interior of Lothlorien )
 * Rivendell (Imladris)
 * The Grey Havens
 * Barad Eithel
 * Himring (after end of the First Age, mostly underwater)
 * Minas Tirith (in Beleriand)(ruined with rest of Beleriand)
 * Gondolin (ruined with rest of Beleriand)
 * Menegroth (ruined with rest of Beleriand)

Fortresses/Strongholds of Dwarves

 * The Mines of Moria (Khazad-dûm)
 * Erebor (The Lonely Mountain)
 * The Iron Hills
 * Belegost (in the Ered Luin, the Blue Mountains)
 * Nogrod (in the Ered Luin, the Blue Mountains)
 * Ered Mithrin (Grey Mountains, later driven out by dragons)

Fortresses/Strongholds of Evil

 * Utumno
 * Angband (with Thangorodrim above)
 * Barad-dûr
 * Dol Guldur
 * Minas Morgul
 * Morannon (the Black Gate of Mordor)
 * Isenmouthe
 * Cirith Ungol
 * Carn Dûm
 * Mount Gundabad
 * Isengard (after Saruman became allied with Sauron)