In antiquity, the production of sea salt was one of the most important sources of salt. According to Pliny the Elder (NH 31.81), the most common way of obtaining salt was through marine salinae: facticii varia genera, volgaris plurimusque in salinis mari adfuso. There are plenty of textual references to marine salt evaporation ponds: Livy (1.33) reported that Ancus Marcius opened saltworks on the Tiber next to Ostia; Pliny (NH 31.84-87) mentioned a series of examples of such installations distributed throughout the Mediterranean, while Columella (Rust. 10.135) indicated the existence of saltworks at Pompeii, and Cassiodorus (Var. 12.24) spoke of those located near Venice. Passages in Rutilius Namatianus (De red. 475-90) and Manilius (Astr. 5.682-92) are also well known for their explanations of how ancient saltworks operated.