The seventeenth-century layout of the Chapel remained unchanged until the seventeen-forties, when Raimondo di Sangro seventh Prince of Sansevero set to work enlarging and enriching the temple. A period of great fervour followed, as he poured into it energy and wealth, working with zeal and skill, calling on renowned painters and sculptors, personally supervising the work, choosing and sometimes creating the materials himself. His idea was to build a majestic temple, worthy of the greatness of the household, enriching it with the finest works of art, but without changing the original structure, attempting to find the best position for the pre-existing tombs in the new layout. This is how works such as the Glory of Heaven, Modesty and the other statues of the Virtues, and the Veiled Christ came into being.
His complex personality, cosmopolitan culture, ingenious invention, his studies in science and alchemy, his Masonic militancy and deep-rooted sense of history made Raimondo di Sangro a generous, but demanding patron. Each individual work, in fact, had to play a unique role in the overall iconographic design that he had conceived, and which the artists themselves were probably unaware of. It is for this reason that in the Sansevero Chapel, more than in any other complex, there is the sense of patronage which, sometimes overwhelming the individual artistic presence, dominates and gives off energy, coherence, a sense of awe, and lends a European air to the whole complex.
The Prince of Sansevero largely maintained the simple architectural structure of the seventeenth-century edifice. The Chapel has a single longitudinal nave with four rounded arches per side; the cornice, constructed using a mastic invented by di Sangro, runs the length of the whole perimeter above the arches. The barrel vault is interrupted by six deep-set windows that light up the whole Chapel. At the top of the apse, the visitor can admire the illusion of a small cupola painted on the ceiling.
In 1901, the Neapolitan tiling floor was finished, enamelled in yellow and blue – the colours of the di Sangro household – a reference to the coat of arms. The beautiful eighteenth-century floor, with its enigmatic labyrinth motif, constructed using a system also invented by the Prince, was destroyed at the end of the nineteenth century. It is still possible to see a sample in the walkway in front of the tomb of Raimondo di Sangro. From there a stair-case on the left leads to the Underground Chamber which the Prince designed but did not live to see finished.
Lastly, on the side door, dating back to the eighteenth century, there is a long and eloquent inscription: “Whoever you are, traveller, townsman, countryman or foreigner, enter and piously pay homage to this prodigious ancient work: this noble family chapel, long since consecrated to the Virgin and greatly enlarged by the illustrious Prince of Sansevero, Don Raimondo di Sangro, to the glory of his forefathers and to immortally preserve his ashes and those of his family, in the year 1767. Observe with attentive eyes and veneration the urns of the heroes endowed with glory and contemplate with wonder this precious homage to the Divine work and the tombs of the departed, and when you have profoundly honoured them, reflect and go your way”.