Marcus Vitruvius Pollio or Vitruvius, was a Roman author, architect, civil engineer and military engineer during the 1st century BC, known for his multi-volume work entitled De architectura. By his own description Vitruvius served as an artilleryman, the third class of arms in the military offices. He probably served as a senior officer of artillery in charge of doctores ballistarum (artillery experts) and libratores who actually operated the machines.