Tuff allowed catacombs, quarries and later burial grounds to develop along the valley edges. Early Christian devotion around saints and bishops connected underground spaces to basilicas and processional routes above.
Baroque palaces and the Basilica of Santa Maria della Sanità record seventeenth- and eighteenth-century investment, while the nineteenth-century bridge carried traffic overhead and altered neighbourhood movement and social geography.
Recent access to the catacombs and heritage sites is closely tied to local organisations and employment. Visitors should recognise community governance, avoid poverty tourism and keep homes, schools and businesses outside the camera unless consent is clear.
Book the catacombs through their official community operator, walk the Holy Mile in daylight and treat the neighbourhood itself as a living place whose access and dignity come before photography.