清嘉慶年間，臺灣府城的文武要員面對前所未有、從海洋來襲的海盜蔡牽集團侵擾時，積極動員位居城外西側海岸、以商業貿易為主之區域的人力、船隻以及資金，來協助府城的防衛。雖然因為商貿而富裕、卻因位處城外而長期被城內官紳視為身份低下的海口郊民們，藉趁著軍事緊急說服官府，讓他們在很短的時間內修築了一座木城，使得原處城外海口空間得以在形式上納入新的大府城範圍之內。這不只是清代府城空間概念的一次大轉變，也是原本的海口以及新的府城社會整合的開始。影響深遠的還有，郊商面對外在軍事威脅以及築城時的社會動員與經費攤派，在事件平定之後成為社會慣習，這強化了「三郊」的社會整合以及經濟力量。

For civil and military officials in Tainan Prefecture, the Jiaqing period of the Qing was unusual. In response to the invasion of Tainan by Cai Qian pirate gang, these officials mobilized manpower, vessels, and funds from Tainan, especially from the wealthy guild merchants inhabited along the coast outside the west side of Tainan city wall. Although these guild merchants had accumulated considerable wealth, their economic strength did not accord with their social status as they were despised by the officials and gentry in the Tainan city. Cai Qian’s invasion created an excellent opportunity for these guild merchants to become city dwellers. In order to defend the pirates, with the official permission, they expanded the city wall to enclose their habitations. This expansion of city area signified a conceptual change in space—the scope of walled area of Tainan prefecture, and also suggested the re-delimitation between the walled and coastal area of Tainan. In addition, these guild merchants’ economic strength increased and thus they became more powerful in the process of social integration after Cai Qian’s invasion. This is because these guild merchants had the legitimacy to mobilize resources from the local society in response to the threat imposed by the pirates, and this practice persisted even after Cai’s invasion. Hence, these guild merchants were empowered.