Key of the Three Moons ( Warcraft III ) Key of the Three Moons is the fourth chapter of the undead campaign , Path of the Damned . Battle . Having destroyed the outer elfgate , Arthas and his army pressed on into the Inner Kingdom , killing all in their path . Sylvanas ordered her forces to retreat over the Elrendar River , waiting alone to confront Arthas personally . She swore that while Arthas had gotten through the first gate , he would never breach the second , since the inner gate to Silvermoon could only be opened by a special key , which she would make sure he will never possessed it . Arthas watched her retreat , sneering that she was wasting her time trying to " outrun the inevitable " . Sylvanas commented she was not running and remarked Arthas had clearly never fought elves before , upon which she used a magic arrow to destroy the bridge , the only crossing point over the Elrendar , thus delaying the Scourge ' s advance . Furious , Arthas ordered his soldiers to find another way across the river . The undead fell upon a small village trapped on their side of the river , slaughtering the helpless villagers , destroying the buildings and raising their own base upon the ruins . Arthas ' s forces were bolstered by two new arrivals : greedy goblins willing to offer their zeppelin s to the death knight , and a new form of solder ; the spider - like Crypt fiend s . These arachnid warriors quickly proved their worth when a force of dragonhawk riders attacked , shooting their webs over the airborne riders , bringing them down and leaving them at the mercy of the undead . Having assembled a substantial force , Arthas used the zepplins to ferry his army to the nearest elven settlement to the east , which the Scourge destroyed swiftly . In the aftermath of the slaughter , Arthas found in the ruins of a temple a strange crystal . The shade of Kel ' Thuzad told him the crystal was part of the Key of the Three Moons , the key required to open the inner elfgate . Knowing now what he needed to do , Arthas quickly reassembled his army and fell upon the next elven settlement , this time to the north . This village offered little more resistance than the first ; it was quickly overrun and Arthas claimed the second crystal from the ruins of the temple there . Finally , the Scourge army fell upon the final elven village to the west . This one proved more of a challenge , for Sylvanas and her army were positioned there , and they fought like ones possessed to defend it . Though the efforts of the high elves delayed the undead for a time , ultimately , the Scourge would not be denied , and the settlement was taken . Sylvanas and her surviving forces retreated back to outposts they held in the forests while the Scourge ravaged the fallen settlement , and Arthas claimed his prize from the ruins of the third temple . With all three crystals in his possession , the Key of the Three Moons was complete and the way onward was now open to the Scourge . Arthas retreated back to his base , where he began to gather his forces for a final assault on the inner elfgate . In a final defiant gesture , Sylvanas obtained some zepplins of her own , as well as more dragonhawk riders , and led them in desperate hit - and - run attacks on the Scourge , hoping to prevent their advance , but ultimately , once a suitable force had been raised , Arthas departed with his army and fell upon the defences of the inner elfgate without mercy . The elven defenders bravely fought to the end , but they were too few and too weakened to put up much of a defence , and were killed down to the last elf . With the defences gone , Arthas used the Key of the Three Moons to blast open the elfgate ; the way to Silvermoon was now open to the dead . Sylvanas ordered her remaining forces to retreat to their holdings on the city ' s outskirts , wondering if there was any way to drive the undead back , while Arthas , growing ever more vexed by the Ranger - General ' s defiance , vowed to deal with her before he marched on the elves ' capital .