The Gate of Babylon: King's Treasure is a dark red, key-shaped shortsword owned by Gilgamesh that connects to his treasury, the "Golden Capital," allowing its user to easily access its contents. It connects the space of reality to the vault, opening an "invisible door" that allows for the contents to pass through upon the user's command. The items that pass through the gate form ripples in the empty air as they appear. They can be summoned anywhere, either directly to the users hands or anywhere in the direct vicinity. The rank changes from E to A++ due to reflecting on the ranks of the various contents of the treasury, and it is also once referred to as an EX ranked Noble Phantasm during Fate/Zero due to containing Ea. The Gate becomes more powerful as the wealth of the owner increases, but if the treasury does not contain a wealth of valuables, then it will not be a useful Noble Phantasm. There is probably a Road of Babylon as well.
This Noble Phantasm is the reason that Gilgamesh is of the Archer class of Servants. The weapons contained in his treasury become bullets upon his command, making him an archer with the strongest arrows. He generally readies numerous weapons at a time, either just letting their hilts stick slightly out of the gate or letting them levitate in the air behind him. Upon snapping his fingers, the seemingly infinite number of weapons can be fired without pause. They move quickly and take aim at the target according to Gilgamesh's will, allowing him to fire them without having to even touch them.
Each weapon has the ability to cause certain death to an opponent, and they are shot with enough force to repel a single swing from Berserker's large axe-sword. While it is possible to block many of the strikes, to do so without knowing the abilities of the weapons can be seen as suicidal.
He starts out with lower numbers of weapons, but increases the number of weapons fired in a volley depending on the amount of respect or anger he feels towards his target. He uses as little as one or two at first while playing with his opponents, but can easily summon over eighty for a single strike when he is serious. Upon firing them, he can allow them to pierce the ground after striking the target, causing a large amount of destruction with each weapon, or he can instantly return them to the vault faster than Shirou Emiya can even perceive during the Fate route. Upon closing the Gate, any weapons left on the battlefield will instantly dissipate and return to the vault. He can leave them out if he wishes, such as when they've been "stained" by striking Caster's summoned creature. The ability to fire the weapons yields an excellent ratio of destructive power to magic energy efficiency due to the cost of prana used to fire the Noble Phantasms as bullets being relatively low. The only real prana usage lies with the Gate of Babylon's activation cost.
He generally fights at long range, though he will wield a single weapon in close combat if he feels confident in his victory. He makes use of the many unknown abilities of the weapons, and constantly switches them to keep his opponent off guard. Still, he is not a swordsman, so he is easily outclassed if an opponent is skilled at close combat. Against something like Unlimited Blade Works, which allows for weapons to be drawn and fired slightly faster than the Gate of Babylon, Gilgamesh finds himself easily outclassed and overwhelmed when forced to fight in close combat.
The treasury contains all of the treasures of the world that he collected during his life, from the finest wine and golden drinking cups, a meat that multiplies in proportion to how much is eaten, and divine mysteries from nearly every legend. Nearly anything can be found within, and the amount of wealth within exceeds even his own knowledge. It contains swords, pole-arms, lances, hammers, shields, demonic swords that later made their way to Europe and South America, and a number of weapons unidentifiable to Shirou from sight, all of which form a perfect treasury of masses of unused weapons that simply went to sleep with the king. Shirou claims that even though he cannot see them all, he can feel that their numbers are infinite. After his death, the contents were spread all over the world after being passed on or stolen, and the treasure, valued because they were splendid swords, eventually became Noble Phantasms. The only item contained in the vault that was not passed on to another user than Gilgamesh is Ea. All of the weapons are technically nameless, the original Prototypes of the Noble Phantasms and the common points before they became objects of faith that act as the foundations for their legends. They are the original models of every legend, myth, and folklore, besides those like Excalibur, which Gilgamesh takes an interest in owning. Shirou states that the quality of the weapons makes the Noble Phantasms used by others look like fakes themselves. While Cú Chulainn has the Gáe Bolg that became famous, Gilgamesh possesses a weapon that later became the Gáe Bolg, but wasn't famous at the time Gilgamesh owned it. If weapons of a previous incarnation meet those that descended from them, such as Gram facing Caliburn, the deteriorated newer model will generally always lose.
It contains numerous A rank weapons, capable of piercing God Hand dozens of times to take eleven of Berserker's lives and then piercing him with twenty-three more weapons afterward. Just a single weapon is enough to pierce Caster's strongest shield, and keep any other another Servant on the defensive. Along with the named weapons, others include an axe, scythe, and scimitar with the ability to seek out their targets at a speed that allows them to match the pace of a jet, swords and spears capable of shattering mountains, swords and hammers larger than a person, a three-edged sword able to arc behind the opponent to attack them from an unguarded position, an invisible sword like Invisible Air, a sickle that drains away prana and deals damage while passing directly through flesh and armor without causing any actual physical damage, and a sword of ice that freezes the space that it cuts. The numerous weapons contain various different effects and abilities, allowing him to assault the weaknesses of any Servant. This places him at an advantage over most Servants in combat, such as attacking Saber with a sword that has an advantage over her dragon blood, or assaulting a Servant with a weapon they were specifically weak against during life.
The many defensive items against magecraft in the gate, such as his golden armor and a reflective mirror shield, make up for his low Magic Resistance under Kirei Kotomine by neutralizing most offensive magecraft. Their defensive power is quite high, as the armor and mirror shield can repel Rin Tohsaka and Illyasviel von Einzbern's extremely strong magecraft completely. He also has very specific artifacts like a defensive armament that protects against the Multi-Dimensional Refraction Phenomenon that is capable of stopping Tsubame Gaeshi. Though, most magi attempting large-scale spells would simply be crushed by a wave of Noble Phantasms before they even had time to cast them.
- Dainsleif is a demonic sword from the Nibelungen, a cursed Noble Phantasm that contains a powerful curse of "reparation" to be used on its target that also drives the fate of its possessor to ruin. It is a demonic sword handed down the family that killed the Northern European hero Sigurd, and it originally among one of the weapons hoarded by the dragon Fafnir. While demonic and holy swords carry with them both glory and destruction, Dainslef is said to only bring the latter onto its master.
- Durandal: The Peerless Sword is the holy sword favored by the paladin leader of the Twelve Peers, Roland. It was granted to king Charlemagne by an angel, and awarded to Roland. It is a dazzling sword that possesses three miracles that allow it to maintain its sharpness even after its possessor's prana is depleted. It is a symbol of power splendidly forged much like Caliburn.
- Ea is the most powerful weapon inside the Gate of Babylon, and it is the one favored by Gilgamesh. He is able to use a rain of weapons to keep the opponent off-guard while preparing to use it.
- Gáe Bolg
- Gram is the sword of the sun wielded by Sigurd, the greatest hero of Northern Europe in the Völsunga saga. It is a demonic sword of glory and destruction that is the model of Caliburn in the legend of King Aurthur and also based on Merodach. Their true natures, the ideas behind their creation, and their souls are very similar. As Caliburn was a "sword stuck in the stone that chooses the king", Gram was also a chosen sword of appointment lodged in the mighty tree of the king of Volsung. The legend of Gram and its master, Sigurd, is a tale ripe with glory and destruction fitting the great hero. The later composed Middle Ages Germany retelling, Der Ring des Nibelungen, is a story of a knight equal to the legend of King Arthur with Gram appearing with its name changed to Balmung. It is the greatest of enchanted swords rivaling the greatest of holy blades, and is even equipped with special dragon slaying attributes damaging towards people such as the king of knights who is the incarnation of a dragon. It uses the same ability as Caliburn, a light the burns away everything it touches, that took seven of Berserker's lives.
- Houtengeki is a one of kind halberd passed down in Chinese culture and the only halberd out of many to attain the rank of Noble Phantasm, probably due to its use by a famous military commander. It is a polearm with many different uses such as thrusting, swiping, pulling, parrying, and various others. It also has a crescent-moon shaped blade, the crecent blade, and weapons with only one of these blades are called Seiryugeki. It is said that a great deal of skill is needed to handle this weapon, though its versatility and ease of use once mastering it allowed for it to be used to serve the appropriate role for any type of combatant. Its use eventually went out of favor as different dynasties rose and fell until it was revived during the Sung period as Houtengeki. It appears in Fate/Extra as God Force.
- Merodach: The Original Sin is the originating sword that eventually led to the legends of both Gram and later Caliburn.
- Potion of Youth was used after the fourth Holy Grail War to allow him to blend into society and be more sociable with those around him. It returns him to an adolescent state, which is why he didn't cause any problems during those ten years. It allows him to retain his memories, though his personality is returned to that of a child. He claims that he doesn't understand the actions of his older self and feels bad about them. It is also used during Fate/hollow ataraxia. He shows the ability to forcibly reverse the effects when facing the horde of Shades.
- Sha Nagba Imuru: The all-knowing, all-powerful star is the Noble Phantasm owned by the child form of Gilgamesh in the Fate/hollow ataraxia card game. It allows him to view some of the cards in the opponent's hand and deck.
- Vajra is a symbol of divinity of Indra, the god of lightning from the Vedic mythology of the ancient India, and the indestructible diamond pounder weapon carried by the gods of Buddhism. Vajra was initially known by its proper name of Vjaya when Indra was first introduced to India as a phenomenon that spread from the Aryans. Along with Indra, whose name changed to Taishakuten, his divine symbol also had its name changed and became known as Vajra after the age of Buddhism as India's main religion began. It is a simple weapon that can only be shot only once for a fixed B+ rank damage separate from the user's prana supply.
- Wine, "the king's wine" as claimed by Gilgamesh, contained in a set of wine bottles made of heavy gold that are inset with sparkling gems. Rider believes that it could not be brewed by human hands, asking if it is a "drink of the gods", to which Gilgamesh affirms by boasting that "Whether wines or swords, only the best is stored in my treasury."