The Battle of Heaven and Earth was a final effort made by the Marleyan military, the Warriors, and remaining members of the Scout Regiment against Eren Jaeger in an attempt to bring an end to the rumbling at Fort Salta. This resulted in the death of Eren Jaeger, Zeke Jaeger, and the anomaly responsible for the Power of the Titans, ending of the rumbling and eliminating the Power of the Titans from the world.
Prelude: Towards the end of the surprise attack from Marley on the island of Paradis, Zeke Jaeger let out a scream that transformed many Eldians into Titans that quickly overwhelmed the surviving Marleyan soldiers. As Zeke went to reunite with his brother Eren, Warrior candidate Gabi Braun shot Eren in the neck and decapitated him; however, the power of the Founding Titan that was residing within Eren saved his life. Due to Zeke making contact with Eren's head, both were sent to the realm where the spirit of Ymir Fritz resided.
The battle: As the flying boat travels towards Fort Salta, Armin notes that due to obtaining the War Hammer Titan, Eren may not be residing within the nape of the Founding Titan and discusses with both the Warriors and Scout members about various means to incapacitate the Founding Titan. Suddenly, they are transported to the Paths and told by Eren that he will not stop the Rumbling and the only way they can stop it is to kill him; after promising not to remove their free will, he transports his former allies back to the flying boat. The Scout Regiment arm themselves with their vertical maneuvering equipment and explosives to detonate at the base of the Founding Titan's head.
Early efforts: As the flying boat travels towards Fort Salta, Armin notes that due to obtaining the War Hammer Titan, Eren may not be residing within the nape of the Founding Titan and discusses with both the Warriors and Scout members about various means to incapacitate the Founding Titan. Suddenly, they are transported to the Paths and told by Eren that he will not stop the Rumbling and the only way they can stop it is to kill him; after promising not to remove their free will, he transports his former allies back to the flying boat. The Scout Regiment arm themselves with their vertical maneuvering equipment and explosives to detonate at the base of the Founding Titan's head.
Battle on the Founding Titan: The group notices that Zeke's Beast Titan dissolved soon after Reiner defeated it, alerting them that Zeke was not inside it. As the others retreat so Armin can transform into the Colossus Titan, he is captured by another Beast Titan that was formed resembling an okapi. Many more Titans begin to spawn atop the Founding Titan's back, which react with hostility and drive the soldiers back.
Source: Battle of Heaven and Earth (Anime), available under CC BY-SA 3.0.