For example, he helped complete the decoration (1857–1860) for the rebuilt basilica of San Paolo fuori le Mura, working on Paul laying on of hands on Barnabas in Antioch and The Magician Elymas in Pafo del Sud.
In 1862 he moved to Arpino to decorate the ceiling of the Palazzo Sangermano, with a fresco depicting Chariot of Venus with some nymphs, for which he was paid 200 scudi.
After the death of Cesare Fracassini, Mariani, along with Francesco Grandi, and Coghetti, were asked to complete the fresco decoration of the newly rebuilt Basilica of San Lorenzo fuori le Mura.
He also frescoed (1870–74) the cupola, lunettes of the counterfacade, and the chapel of the Crucifix of the church of Santa Maria di Loreto alla Colonna Traiana.
In Teramo, he also painted a triptych depicting the Virgin Enthroned with Saints Francis and Anne for the Savini chapel, and decorated the palace city of the same family.
[4] In 1878, he won a contest to paint the main Hall of the Finance Ministry, where he depicted an allegory of the Unity of Italy with Illustrious Men of Past and Present.
Mariani gave drawing lessons to the Prince of Naples Vittorio Emanuele and was commissioned to paint a frieze in the Royal apartments of the Palazzo Quirinale.
For Santa Lucia del Gonfalone, he painted frescoes with three scenes: The Vision of St Bonaventure, Pope Sixtus V blesses the Redeemed Barbary Slaves, and The oath of Giovanni Cerrone.
In 1867, he was commissioned by Signore Baldini Giustiniani to paint frescoes at the Castello at Rocca di Lanciano, depicting Aurora and the Chariot of the Sun.
In 1870, he became a member of Academies of Fine Arts of many cities in Italy, including Perugia, Florence, Milan, Urbino, Carrara, Orvieto, and Ravenna.
The last official task of the artist was to participate in 1896 in the juried competition, "Per una memoria sulla tecnica dei dipinti", launched by the Ministry of Education public, replacing Francesco Jacovacci.