The Danavas named Nivatkavachas, who are hard to be vanquished in battle (also live here.) You know how Shakra is not able to cope with them.
निवातकवचा नाम दानवा युद्धदुर्मदाः। जानासि च यथा शक्रो नैताशक्नोति बाधितुम्॥