The lower register of the enclosure is decorated with a vegetal frieze composed of scrolls starting from a luxuriant acanthus bush; a vegetal candlestick rises vertically from the centre of the acanthus.
Ivy, laurel and vine leaves grow from the whorls of the acanthus, tendrils and palmettes sprout, and where the stems thin, winding spirally, bloom flowers of every variety.
The thick vegetation is home to small animals and twenty swans with outstretched wings, which mark the rhythm of the composition.
This vegetal relief was often referred to the 4th Eclogue of Virgil, where the seculum aureum, the return of the happy and peaceful age is announced with the abundant and spontaneous production of fruits and harvests. Beyond the generic reference to fertility and abundance, resulting in the return of the Golden Age, the frieze can also be read as an image of the pax Deorum, the reconciliation of the divine forces governing the entire universe, made possible by the advent of Augustus.