An invading army would have to overcome the Bloody Gate at the mouth of the Vale before taking the Gates of the Moon.

The Eyrie is only a small castle itself, but is almost impossible to reach. It is inhabited by the Arryns during the long springs and summers, before the family removes to the Gates of the Moon at the bottom of the mountain to sit out the winters. In the A Song of Ice and Fire novels, the Eyrie is a mountain-top fortress located on a shoulder of the Giant's Lance, one of the tallest mountains on the continent. Map showing the location of the Eyrie on the continent of Westeros. The Eyrie in Season 4 behind the Bloody Gate In the books In Season 1, it was shown as a tall, thin building upon a single spire of rock, while in Season 4, it is a somewhat squatter (though overall just as large) building perched atop a pair of rocky outcrops. The exterior of the Eyrie has been visibly retconned from its Season 1 look to its reappearance in Season 4. Production Designer Gemma Jackson said of creating the set for the Eyrie that, 'A lot of the mosaics in the Eyrie were based on a beautiful chapel I visited in Rome.' Executed by Arya Stark for his many crimes against the North. Lord, widower of Lady Lysa and former Lord Protector of the Vale.It proved impregnabe by the hostile Hill tribes. He ruled from the Eyrie as King of Mountain and Vale and it became the seat of House Arryn, whose head was also the Lord of the Eyrie. The Eyrie was the ancestral seat of the First Men Mountain Kings until the Andal Invasion, where it was won by Ser Artys Arryn after the Battle of the Seven Stars. There is a very slight slope in the cells, and prisoners must be careful not to roll out of the cell in their sleep and plummet to their deaths. Prisoners at the Eyrie are incarcerated in the sky cells, cells which are open on one side to the air. Being thrown through the Moon Door is the preferred method of execution at the Eyrie, and is a particular amusement for the intellectually stunted Robin Arryn. A notable feature of the chamber is the Moon Door, a hatch built into the floor through which people can fall to the floor of the Vale far below. The High Hall of the Eyrie is the main audience chamber, where the Lord of the Vale greets visitors from a throne made of weirwood. It is currently the seat of Robin Arryn – the Warden of the East. For these reasons, the Eyrie is considered impregnable to any attack that does not involve dragons, and its defenses have never been overcome. Those who would approach the Eyrie must pass through three way-castles guarding the ascent - and then, must proceed in single file, making them very vulnerable to archers. It is approached by a narrow causeway and road. The Eyrie straddles the top of a peak in the Mountains of the Moon several thousand feet above the valley floor below. It is located in the Vale of Arryn near the east coast of Westeros. The Eyrie is the principal stronghold of House Arryn. One of the Eyrie's sky cells, shown from the inside. They say it's impregnable.' Bronn: ' Give me ten good men and some climbing spikes, and I'll impregnate the bitch.' - Tyrion Lannister and Ser Bronn of the Blackwater

Runestone keeper gods