St. Peter's dome
Between 1743 and 1748, Vanvitelli and Poleni worked to strengthen the dome by inserting six iron rings into the tambour and calotta, the largest of which measured 60 m in diameter. Nicola Zabaglia, a simple illiterate man whose extraordinary empirical knowledge of mechanics enabled him to build the scaffolding necessary to put the circles in place, also made a major contribution to these improvements. Around that time, Clement XI commissioned the publication of a magnificent and richly-illustrated work (ultimately completed under Benedict XIV and funded by the Fabbrica di San Pietro, with words by Lelio Cosatti and sumptuous artwork). The book paid rightful homage to Nicola Zabaglia, the humble carpenter so instrumental to the construction of the world’s biggest church.
Nicola Zabaglia, Castelli e ponti di maestro Niccola Zabaglia con alcune ingegnose pratiche...,Roma 1744