  A search for resonant Higgs boson pair production in the $b\bar{b}b\bar{b}$
final state is presented. The analysis uses 126-139 fb$^{-1}$ of $pp$ collision
data at $\sqrt{s}$ = 13 TeV collected with the ATLAS detector at the Large
Hadron Collider. The analysis is divided into two channels, targeting Higgs
boson decays which are reconstructed as pairs of small-radius jets or as
individual large-radius jets. Spin-0 and spin-2 benchmark signal models are
considered, both of which correspond to resonant $HH$ production via
gluon$-$gluon fusion. The data are consistent with Standard Model predictions.
Upper limits are set on the production cross-section times branching ratio to
Higgs boson pairs of a new resonance in the mass range from 251 GeV to 5 TeV.
