  The iron-based superconductors are characterized by strong fluctuations due
to high transition temperatures and small coherence lengths. We investigate
fluctuation behavior in the magnetic iron-pnictide superconductor
$\mathrm{Rb}\mathrm{Eu}\mathrm{Fe}_{4}\mathrm{As}_{4}$ by calorimetry and
transport. We find that the broadening of the specific-heat transition in
magnetic fields is very well described by the lowest-Landau-level scaling. We
report calorimetric and transport observations for vortex-lattice melting,
which is seen as a sharp drop of the resistivity and a step of the specific
heat at the magnetic-field-dependent temperature. The melting line in the
temperature/magnetic-field plane lies noticeably below the upper-critical-field
line and its location is in quantitative agreement with theoretical predictions
without fitting parameters. Finally, we compare the melting behavior of
$\mathrm{Rb}\mathrm{Eu}\mathrm{Fe}_{4}\mathrm{As}_{4}$ with other
superconducting materials showing that thermal fluctuations of vortices are not
as prevalent as in the high-temperature superconducting cuprates, yet they
still noticeably influence the properties of the vortex matter.
