The Talon Gates were what was thought to be two long rocks standing in the sea of the Madaran Empire, close to the delta of the Suido River and the village of Sekana. In reality they were all that is left from the leviathan Nicol Bolas fought in the first planeswalker duel in Dominaria.
In ancient times, the Talon Gates served as a sort of focal point for various changes throughout the multiverse. Due to Ravi ringing her Apocalypse Chime, the boundaries between the planes of Dominaria and Kamigawa were weakened. During the fall of the Madaran Empire, the Talon Gates were the main way of traveling between Madara and the Edemi Islands.
It is also this place where the Madaran rift was located. During a fight between Nicol Bolas and Leshrac the Talon Gates were destroyed by the Nightwalker, but shortly after his defeat they were recreated by Bolas.