Ligillium was an ancient site reputed to hold the fabled Zaterl emerald.

In 2367, Captain Jean-Luc Picard offered to take "Ardra" (in fact a con artist) to the ruins of Ligillium if she accepted arbitration on the Contract of Ardra. Her interests however lied elsewhere, as she stated she had "enough jewels". (TNG: "Devil's Due")