chordae obliquae

The "slanted strings" are commonly identified as an angular harp deriving from the Near East and Egypt, the sambuca, described by the 2nd century CE Greek scholar Athenaeus as a four-stringed instrument invented by the Syrians (see Greek stringed instruments). Oriental harps such as the sambuca, trigonum, psalterium, and spadex produced a distinctive high piercing sound. Similar to modern harps, these were triangular in shape and most were played by tipping the pointed end of the instrument to the ground. While they were known to and used by the Romans from at least Plautus' time (see Stichus 380-1 for the sambuca in the cargo of a Phoenician ship), they never lost their "foreign" association (see Livy, AUC.39.6.7; Quintilian, Institutio Oratoria1.10.31).
Umbricius scornfully groups all oriental harps, despite their differences, under the term chordas obliquas, refusing to grace with their names the stringed instruments that flow west from the Orontes River into the Tiber.