Tidal marshlands and the Frisians are a dual entity. It's on these treeless salt marshes the Chauci and the Frisii (Frisians) dwelled when the Romans arrived around the year of Christ. People lived on terps (artificial settlement mounds) and would continue to do so till this very day. It was the Roman soldier, Plinius (or Pliny) the Elder, who described this terp culture in his Naturalis historia, written in the first century AD. Then, the terp region encompassed the area what's today provinces Friesland and Groningen in the Netherlands and the region Ostfriesland in Germany. The Chauci generally are situated in Ostfriesland and possibly part of province Groningen too. The Frisii were the neigbouring tribe living west of the Chauci, more-or-less provinces Friesland and Noord Holland.
Below what Pliunius the Elder wrote about the Chauci, about the terp culture of the Wadden Sea.
"We have discussed that at least in the east there are several peoples along the coast of the Ocean who have to live without trees and shrubs. And we have also seen such peoples in the north, namely the Chauci, both the Great Chauci and the Smaller Chauci. Twice a day over an immeasurable distance the Ocean comes up with enormous amounts of water and covers an area eternally disputed by nature, and of which it is unclear whether it belongs to the mainland or is part of the sea.
There, this poor people occupy high dwelling mounds or dams that they single-handedly have raised to the highest water level they experienced. With their huts they have built on it, they look like sailors when water covers the surrounding land. But they look like shipwrecked when the water has withdrawn, and they hunt around their huts for fish that flee with the sea.
They cannot keep cattle and feed on milk like neighbouring peoples. And because no scrub grows in the wider area it’s impossible for them to fight with wild animals. From reed and bulrush, they weave rope to tie fishing nets. They collect mire by hand that they let it dry through the wind, more than through the sun. And with this peat they heat their food and their bodies churned by the northern wind. They only drink rainwater, which they keep in pits at the entrances of their house.
And these peoples speak of slavery when they are conquered by the Roman people today! That is indeed how it goes: fate leaves many people alive to punish them."
Plinius or Pliny the Elder
Note 1: the mire must have been cow dung. Cow dung can be dried and then used as fuel. This was practiced in the terp region of North Frisia, or Nordfriesland, in Germany after the Second World War still. The other option is he actually meant peat instead of mire, but then you're already a bit more inland away from the terps.
Note 2: That the Chauci (and the Frisii) didn't have cattle is incorrect. To the contrary, the people of the tidal marshlands were livestock farmers par excellence. No explanation as to why Plinius missed this 'detail'.
Note 3: The pits filled with rain water (probably collected from the roofs) might refer to what is known in North Frisia or Nordfriesland in Germany as a Fething or in Mid Frisia (i.e. province Friesland) in the Netherlands as a dobbe. Check out our blog post Groove is in the Hearth too about collecting rain water with grooves at terps, and all the superstitious and pagan practices that were part of it. Fethings and dobbes are now mainly used for the sweet water supply for cattle.
Suggestions for further reading:
Gelder, van J. et al., Plinius. De wereld. Naturalis historia (2004)