Transverse band
Transverse band also known as the transverse atlantic or atlantal ligament: attaches to a small tubercle on the medial cortex of the C1 (atlas) lateral masses on both sides anterior to the tectorial membrane and dura. It passes posterior to the dens, with a small intervening synovial capsule, fixing the dens to the posterior margin of the anterior arch of the atlas. It is the strongest ligament in the whole spine 1) and arguably the most important!
With the alar ligament, the transverse band is the primary stabilizer of the atlantoaxial joint 2)