The story
From the Hanyu Pinyin romanization of the Mandarin Chinese pronunciation for 天安門／天安门 (Tiān'ānmén), literally "the gate of Heaven's peacemaking" or conventionally: "the gate of heavenly peace", without syllable-dividing mark (隔音符號／隔音符号 (géyīn fúhào)).
Etymology from Wiktionary, CC BY-SA 4.0.