During his early years in Rome, where he arrived at the age of fifteen, Dosio produced numerous drawings of the ancient and modern city, and developed a reputation as an antiquary while he was still a young man.
In 1562 he was carrying out an excavation on behalf of the papal condottiere Torquato Conti, who had extensive contacts among humanist and antiquarian circles in Rome and knew Dosio's good friend Annibale Caro.
Dosio was uncovering the fragments of the marble map of Rome made for Septimius Severus, the Forma Urbis Romae from a site near the Church of SS Cosma e Damiano.
[2] In 1564 a papal courier found Dosio in the Umbrian hilltown of Amelia, working on a funeral monument for a local bishop, Bartolomeo Farrattino.
The overall design of the fortifications was doubtless due to Pius's cousin, Gabrio Serbelloni, and the military governor, Torquato Conti, to whom Dosio owed the commission.