Down-the-barrel Mg I and Mg II absorption towards G1, G2, and G3 (top panels), and intervening absorption towards the Arc, Ci1, Ci2, and the quasar (middle and bottom panels). The normalised binned fluxes and 1σ uncertainties are shown in, respectively, black and grey, with the absorption lines highlighted in purple (top) or blue (middle and bottom). The zero point of the velocity scale corresponds to z = 1.167.