When two years ago a group of senior Catholic bishops from several countries made their now annual visit to Gaza’s tiny but still lively Christian community, they were welcomed to a Friday Mass at the Holy Family Latin Church by the Brazilian parish priest, Fr Mario Da Silva. Pointing out that Pope Francis had designated 2016 as “the Year of Mercy”, and that visiting prisoners was one of the seven corporal acts of mercy, Fr Mario added with something of a flourish: “Thank you for visiting the biggest prison in the world.”