Achasanseong, Mountain fortress in Gwangjin District, Seoul, South Korea.
Achasanseong is a fortified site on the summit of Achasan Mountain in Seoul, featuring stone walls distributed across the plateau. The fortification follows the natural terrain and offers views of the city in multiple directions.
The site originated during the Three Kingdoms period and was successively controlled by Baekje, Goguryeo, and Silla. A notable event was the death of Goguryeo general Ondal there during a battle.
The site preserves traces of three different kingdoms visible in its structures and layout. Visitors walking through the grounds can observe how each ruler adapted the space according to their own military and defensive concepts.
The site is accessible via marked trails that lead to different sections of the fortification and feature information panels. Good footwear is recommended as paths cross stone and earth terrain with some elevation changes.
The walls display an uncommon mix of construction techniques as each of the three kingdoms brought its own building methods and design ideas. Recognizing these layers requires close observation but reveals much about military development during this period.
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