Longitudinal spin structure of the nucleon at COMPASS

For a large fraction of its already twenty year long existence, the COMPASS collaboration hasstudied the polarised structure of the nucleon via muon-nucleon scattering. This paper summa-rizes the final results obtained in longitudinally polarised DIS, either inclusive or semi-inclusive.For inclusive DIS, these cover the measurements of structure function $g_1$, and the information ex-tracted from them in terms of polarised PDFs (pPDFs) and Bjorken sum rule. From $g_1$ measure-ments alone, combining COMPASS with world data, the quark spin contribution to the nucleonspin is determined to be 0.26 < ∆Σ < 0.36. And from COMPASS data alone, the Bjorken sumrule is verified to 9% accuracy. In semi-inclusive DIS, more information can be gained on the pPDFs of sea quarks and gluons. A selection of our achievements along this line are reported.