After his father's death in 1677, the Dowager Marchioness took up the responsibility of overseeing the education of her children: she envisioned a career in Letters for D. Rodrigo, accordingly, she assigned to him the distinguished Latinist scholar Inácio da Silva as a teacher.

During the War of the Spanish Succession, as Peter II of Portugal allied himself with the English and the Germans to prevent a dynastic union between France and Spain under Philip, Duke of Anjou, the Marquis of Fontes served as mestre de camp of the Old Tercio of Setúbal from 1703 to 1706.

[3] The Marquis of Fontes left for Genoa on 9 January 1712, aboard the carrack La Madonna delle Vigne, commanded by Giovanni Lorenzo Viviani, accompanied by his family[1] and protegés such as the young painter Vieira Lusitano.

[4] After a turbulent and stormy voyage (especially while crossing the Gulf of Lion, which motivated a landing in Cagliari in Sardinia, from where passengers and crew made a brief barefoot procession to the Shrine of Our Lady of Fair Winds where the Marquis left a gold ingot worth 500 thousand réis as votive offering), they reached their destination on 30 March.

Travelling the rest of the route by land, they arrived in Rome on 21 May 1712,[1] in time to attend, the following day, the Canonisation Mass of Saints Catherine of Bologna, Pope Pius V, Andrew Avellino, and Felix of Cantalice.

The ambassador then formally presented his letter of credence, relayed the Pope news of the birth of a new Infante of Portugal (Carlos of Braganza), and gave a full account of "the powerful rescue that [King John] was sending to defend Italy, formidably threatened by the Ottoman might".

King John's good fortune with the papacy and Italy would continue to raise the next year, in 1717, when the aid of a Portuguese squadron of ships helped win the Battle of Matapan, in the ongoing Ottoman-Venetian War.