Only a Grandmaster from the second realm of Inborn could maintain the Five External Bodies for more than an hour— it's impossible for those from the first realm.
Only then could it make sense for Marquis of Wuan Bai Mengyang to be able to defend the solitary city against four Inborn Grandmasters, making the city's defense impeccable and unbreakable.
Not to mention the difference in combat power between the second realm and first realm Grandmasters, the ability to maintain the Martial Arts External Body alone has more than doubled in duration.
With such an advantage, it's enough to wear down many first-realm Grandmasters.
If the difference in combat power is also taken into account, it is understandable that a second-realm Grandmaster can face four first-realm Grandmasters in battle with the help of a large army.
"However, although I don't have the strength of an Inborn second-realm, I do have the aid of Immortal Techniques.