Seosamchi, literally meaning the Western Bastion, is a structure projecting outward from the wall, designed to repel approaching enemies. Hwaseong Fortress comprises 10 bastions, and one of them is Seosamchi, measuring only about four meters wide.

Seosamchi is a Chiseong located between Seoporu or the Western Guard Pavilion and Seonamammun or the Southwestern Secret Entrance. Chiseong structures were typically built solely with Seonggakwi. However, due to the uneven ground, various facilities were installed to protect the fortress, resulting in curves and sharp edges within the fortress walls. Seosamchi is characterized by its Seonggakwi, which slightly bends inwards towards Hwaseong Fortress. Seonggakwi served as a low wall within the fortress, enabling Joseon soldiers to defend themselves while repelling enemy attacks.