The Marsaci or Marsacii were a tribe in Roman imperial times, who lived within the area of the Rhine–Meuse–Scheldt delta, under Roman domination. (The river Meuse is the Maas in Dutch, and this name is also often used in English. It Latin sources it is called the Mosa.)
The only relatively clear source concerning the location of this tribe is Pliny the Elder's Natural History. They are in a list of tribes living in the "Gaulish islands" within the river delta region between different mouths of the Rhine. First he mentions the islands of the Batavians and the Cananefates, and then he gives the list of people who he says are stretched out along 100 Roman miles, between the mouths Helinius and Flevus.
The Helinius (or Helinium) is understood to be the main mouth of the Meuse, where the main water of the southern branch of the Rhine, the Waal (Latin Vacalis) also discharged. Flevus (or Flevum) was a Roman fortification on the Ocean, north of the Rhine, mentioned by Tacitus, and equated today with Velsen. Although the details are no longer clear there was apparently a northerly outlet of the Rhine here, north of the main Old Rhine. But the term Flevo was also have used by Pomponius Mela to refer to the fresh water lakes which were in the area of the modern Zuiderzee, which Mela specifically says that the Rhine fed into, perhaps through an ancient version of the Vecht, or the Ijssel. So the Rhine mouth mentioned by Pliny might have been a discharge into a lake, or perhaps water running to Flevum on the coast may have arrived from the Rhine, via the lakes.
- The Frisii are traditionally treated as the ancestors of the modern Frisians, although this is questioned, and they also did not necessarily live in the same part or parts of what is now the Netherlands. Pliny is describing them being far to the south of medieval and modern Frisia. But Tacitus describes there being two populations of them.
- The Chauci are thought to be ancestors of the later Saxons who, according to Tacitus, inhabited a large part of northwestern Germany, north of the Rhine. A part of their population stretched into the east of the Rhine delta area, and had contact with the Roman empire.
- The Frisiavones, perhaps related to the Frisii, appear twice in Pliny, once amongst the delta island dwellers, and once amongst the tribes living to the south, in Belgic Gaul. For this reason they appear to have lived in the southeast of the delta, towards modern Belgium, neighbouring the Batavians, the Tungri, and possibly the Betasii and Sunuci.
About the Marsacii other records mention them being effected by the Batavian revolt confirming that they lived close to the Batavians. Also, like the Batavians and Cugerni, the Roman emperors recruited their horse guard from both the Frisiavones and the Marsacii.
It has been claimed on the one hand that there might be a link to an earlier named Germanic tribe, from far to the east, known as the Marsi. Somewhat more positively considered is the proposal that the name of the Marsacii is preserved in the name of a medieval gau which was named Marsum. This was to the north of the mouth of the Maas into the North Sea.
- A Complete Latin Transcription of Naturalis Historia
- A Complete English Translation of Naturalis Historia (1855)
- A Complete Latin Translation of Tacitus' Germania
- Plin. Nat. 4.29
- Pliny the Elder. The Natural History (eds. John Bostock, H. T. Riley, Esq., B.A. 1855) Book IV. An account of countries, nations, seas, towns, havens, mountains, rivers, distances, and peoples who now exist of formerly existed. Chap. 31. (17.) - Gallia Belgica. In English, or in Latin: "a scaldi incolunt texero texuandri pluribus nominibus, dein menapi, morini ora marsacis iuncti pago qui gesoriacus vocatur".
- Tac. Ann. 4.72
- Germania By Cornelius Tacitus, 4.72
- Smith, William (1854), Dictionary of Greek and Roman Geography