This article marks the start of a series of contributions on Roberto Longhi, presenting various aspects – some better-known, other less so – of the human and critical vicissitudes of the greatest art historian of the 20th century. Here, the focus is on Tanzio da Varallo, an artist that Longhi had greatly admired since his youth. In particular, the history of the ownership of a masterpiece by the painter from Valsesia is reconstructed, the 'Saint Benedict among the Brambles', which, after being untraceable for a long time, now belongs to the Cerruti Foundation in storage at the Castello di Rivoli (Turin). A text by Longhi dating from the mid-1950s is the starting point for an examination of the peculiar mannerism characterising North Italian painters in their relations with culture from north of the Alps.