I was surprised to find not just one, but two fifth-foot spondees in Ausonius’ Versus Paschales, found under heading IV in Green’s edition–a poem of only 31 lines. Moreover, the two lines come in quick succession, only separated by one line. Here are lines 21-5:
trina fides auctore uno, spes certa salutis
hunc numerum iunctis virtutibus amplectenti.
tale et terrenis specimen spectatur in oris
Augustus genitor, geminum sator Augustorum…
Update: Upon looking through Green’s commentary, I realized I missed a third spondeiazon, which comes only three lines after the last one mentioned:
…omnia solus habens atque omnia dilargitus. (28)
This really is remarkable–three spondeizontes within six lines?
For readers interested in the interpretation of this poem (and it is, to my mind, a very interesting poem), Green points us to the treatment of J.-L. Charlet entitled ‘Theologie, politique et rhetorique: la celebration poetique de Paques a la cour de Valentinien et d’Honorius, d’apres Ausone (Versus Paschales) et Claudien (de Salvatore)’, found on pp. 259-87 in La Poesia tardo-antica: tra retorica, teologia e politica (Messina 1984).