A Vestal's thirty years of service were divided into three distinct stages, and her single most important daily task was keeping a fire from ever going out.
A career with three phases
A Vestal's service was traditionally structured across roughly thirty years: an initial decade learning her duties, a second decade actively performing them, and a final decade teaching newer Vestals, a formalised career progression more structured than most religious roles held by women, or indeed most men, in Roman society.
Guarding the flame, and the Palladium
The Vestals' central responsibility was maintaining Rome's sacred hearth fire without interruption, understood as symbolically tied to the continuity and safety of the city itself, and tradition also credits them with safeguarding the Palladium, an ancient sacred image said to have been brought from Troy, kept within their temple's innermost, restricted space.
What still stands in the Forum
The ruins of the House of the Vestals, adjoining the temple in the Roman Forum, still display a row of statue bases and several surviving statues honouring individual Vestals, physical evidence of the honour bestowed on the office even as this entry's companion article addresses the severe punishment awaiting any Vestal found to have broken her vow of chastity.