The Stone of Tear is an immense fortress, believed to be mankind's oldest surviving stronghold and indeed oldest existing structure, having been erected shortly after, or during, the Breaking of the World. It was built by Aes Sedai using the One Power: Earth, Air, and Fire fusing stones together without joint or mortar. The Stone resembles a great mountain and towers over the city of Tear. Only the White Tower is taller.
From the description given in Rand's trip trough the glass columns of Rhuidean about the time of the Breaking it can be guessed that the Stone was built with the main purpose to host and protect Callandor (see below about the Heart of the Stone).
Defending the Stone
The Defenders of the Stone are the elite military group used specifically to guard the Stone. Only Tairens are accepted into the Defenders and officers are usually of noble birth.
The Stone has its own docks, and is an essentially self-sufficient citadel. The inside of the fortress is intentionally complex with multiple hallways joining at odd intersections in order to confuse invaders and provide defenders with even more of a territorial advantage. Arrow slits are the only sizable windows, and any attempt to reach them would only succeed if the person trying was not spotted by the towers (obviously the arrow slits are a later modification, when the kind of warfare was less advanced than the time when the Stone was initially built).
It can be guessed that the ancient Aes Sedai put many Wards to prevent the possibility to Travel directly inside the Stone (but the loss of this Talent made them useless, and the wards progressively went off, without anybody noting it). Alternatively, we can theorize the presence of a no longer functioning Dreamspike.
The Stone had never fallen until the coming of the Dragon Reborn with the help of the Aiel, who were able to gain entry through their skill in stealth and in climbing walls that most would consider impossible to. Matrim Cauthon also managed to force entry by blowing open an arrow slit with explosives in order to rescue Elayne, Nynaeve, and Egwene from their cell after their capture by the Black Ajah.
Heart of the Stone
In the bowels of the fortress is the Heart of the Stone: a great round room with a ceiling supported by red stone columns. Before the Dragon Reborn came, Callandor floated, hilt-down, in the center of that room. No one except the High Lords were allowed to enter the Heart, and even they rarely did so: four times a year for the Rite of Guarding there, and also to raise a Lord of the Land to the office of High Lord. Given the Tairens' aversion to anything relating to the One Power, if the High Lords could have managed to forget that the Heart of the Stone and Callandor existed, they undoubtedly would have.
After the Dragon Reborn came, the crystal sword spent some time wedged into the floor, loaded with a variety of deadly traps to prevent interference, before Jahar Narishma was sent to retrieve it. Afterwards, the great room lay empty.
The Stone also houses a collection, second only to that of the White Tower, of ter'angreal (and a angreal) in a chamber known as the Great Holding. It is not known exactly why the Tairens have collected such an array; perhaps to prevent their use by Aes Sedai, or maybe to diminish by comparison the knowledge that they possess one of the greatest sa'angreal in Callandor, whose drawing by the Dragon Reborn will herald the coming of another Breaking of the World.
A particularly noteworthy item held in the Great Holding is a tall, twisted redstone doorframe, once owned by Mayene, leading to the land of the Aelfinn. Rand al'Thor, Mat Cauthon, Moiraine Damodred and Moridin have all passed through this doorway seeking answers to three questions, or for other goals.
Gates of the Stone
The east gate of the Stone is called the Dragonwall Gate. It has a stable nearby. Like all the gates, is approached from within the stone through a long dark tunnel.