When the Fantastic Four met the Inhumans, Black Bolt argued with Mister Fantastic, encouraging him to leave peaceably, Maximus sealed the refuge in a "Negative Barrier" after discovering that Inhumans and humans were of the same race. 
With his brother insane, and the key to the barrier trapped within Maximus' diseased mind, the Inhumans sought frantically for a way to escape the Negative Barrier. Black Bolt's first attempt was to use his own energy to empower a bomb that would burst it open, but it almost destroyed the entire city before he used his powerful voice to stop it. 
Attilan remained free of any sort of barriers for years and the hidden city was eventually relocated to the Blue Area of the Moon.  However when the city's artificial atmosphere was compromised, the Fantastic Four saved it by shrinking Attilan down in size and recovering it. This occurred during a time that the sorceress known as Morgan Le Fay had risen the undersea kingdom of Atlantis from above the ocean floor and formed an alliance with the Inhuman's Genetic Council.  They had recovered the shrunken city of Attilan,  Although the Fantastic Four, Inhuman royal family, and their allies defeated Le Fay and the rogue Genetics Concil, a new Negative Zone barrier was erected around Attilan, trapping the Terrigen Mist which was unleashed inside, leaving all those still trapped within constantly exposed to the mists.  However eventually, Black Bolt regained the Inhuman throne, contained the mists and took down the barrier, although the circumstances behind this are not recorded at this time.