Mount Othrys

Mount Othrys was the base of the Titans during the First Olympian War and the Second Olympian War. In the First War, it was assaulted by the Olympians, where Zeus used Kronos' scythe to cut him into a thousand pieces, and cast him into Tartarus. Mount Othrys was located on Mount Tamalpais in Marin County and it is said to be made of black marble. Many statues of Titans, also said to be made out of the same black marble that Mount Othrys is made of, lay throughout the palace on top of Mt. Othrys.

The Titan's Curse
When Percy Jackson, Thalia Grace, and Zoë Nightshade find Artemis (who had previously been missing), she is trapped under the sky next to the growing ruins of Mount Othrys. Atlas fights against Percy, who then takes Atlas' burden (the sky) from Artemis so that she can join the fight. Zoë tries to protect Artemis from her father, Atlas, but in his rage, he threw her into the ruins eventually leading to her death.

Percy and his friends see the ruins of the mountain being magically re-constructed - which meant Luke Castellan, with the help of Kronos, was raising Mount Othrys.

The Battle of the Labyrinth
Mount Othrys is in the process of being restored, with the Titan fortress on the top. Kronos returns to the mortal world, in the host body of Luke, due to Ethan Nakamura swearing allegiance to Kronos and renouncing the gods. However, Rachel Dare throws a blue hair brush at him and Luke regains control and yells in pain, allowing the others to escape.

The Last Olympian
Following the defeat of the Titans, Mount Othrys supposedly fades on its own as the Titans were beaten.

The Lost Hero
It was revealed that the Roman demigods assaulted Mount Othrys during the Battle of Manhattan and destroyed the palace. Jason Grace, demigod son of Jupiter, was personally responsible for bringing down Mount Othrys' guardian the Titan, Krios. Jason remembers this near the end of his mission with Piper McLean and Leo Valdez. The campers of the Greek Camp Half Blood were led to believe that it crumbled due to the defeat of Kronos, but they found out when Jason revealed it to them after remembering it. Jason also led the Romans into battle as praetor.

The Second Olympian War
Towards the middle of the Percy Jackson and the Olympians series, it seemed as if Luke, under the influence of the Titan Lord, Kronos (father of time and the Olympians), raised Kronos from the depths of Tartarus in the Underworld. Kronos wanted to retake the control of the power of Ancient civilization from the gods and return humankind to the time when he was the Lord of the Titans. His plan was to wage war on the Olympians, and by going to New York City, where the Empire State Building and Olympus are located, he could destroy their seat of power.

However, with the help of the demigods from Camp Half-Blood and nature spirits, the Olympian gods managed to both defeat Kronos and the monster, Typhon. Mount Orthys was destroyed by the demigods of Camp Jupiter.

Trivia

 * In Greece, the original Mount Othrys is located a few kilometers south of Mount Olympus, but in America it is located on the other side of the country.
 * Even though Mount Othrys is destroyed, Atlas is left to hold the sky.
 * Annabeth said that she could not live in San Francisco because Mount Othrys is right there, and it is not safe for a demigod to live there. This would have been a cover up as Camp Jupiter is located in that area.
 * While Greek demigods thought that Mount Othrys just crumbled into ruins, Roman demigods thought that Kronos just disappeared, but actually the Greeks destroyed Kronos and his army, and the Romans destroyed Mount Othrys.
 * The entrance to Camp Jupiter is based in San Francisco so the Roman demigod camp can keep an eye on Mount Othrys.