Indeed the Roman empire's northern borders ran along the great rivers, which practically cut modernday the Netherlands in half. Territories to the north of these rivers remained unconquered. Some of the peoples who lived there like the Frisians and the Batavs entered into official alliances with the Roman Empire. This did not always end well. The Batavs for instance grew tired of Roman arrogance and dominance (due to ever rising taxes and demand for military service they felt they were being more and more treated as a conquererd people than as the allies they were) so they revolted. Their leader Civilus, who was a roman educated army commander re-germanised his people (they again took up their germanic customs)and set out the free his people (and plenty other tribes and peoples in theprogress)from Roman (cultural and military) dominance. In doing this he was quite succesfull partially by using roman military tactics against the romans. In a very short period of time he succeded in "liberating" most Roman lands North of the Alps and east of the great rivers. This "Germanic" freedom didnt last long though, after a couple of years the Emperors had enough and sent a big army north to root out this rebellion. They steadily marched north reclaiming the lost territories along the way and finally entered into negotiations with Civilus somewhere near the Batav heartlands (there is a famous painting (though painted much later ofcourse) showing Civilus negotiating with a Roman commander on an old crumbled bridge). Talking didnt help and the Rebellion was finally put down with the razing of Batavodorum, Civilus' capital. Civilus himself was in a typical Roman fashion not punished for his transgression but given a promotion and appointed somewhere far away from his own tribe.

I hope this informs you a little more on life in Roman Netherlands. The Batav heartlands are a region in nowadays Netherlands called the Betuwe, and Over Betuwe. My home town of Nijmegen (Novio Magum in Latin) ows its existance to the Romans who gave an Batav settlement the right to hold markets (hence the name) and acknowledged its military value by appointing 2 complete legions to the town