The Iron Age brought a measure of prosperity to the people living in the area of the present-day Netherlands. Iron ore was available throughout the country, including bog iron extracted from the ore in peat bogs (moeras ijzererts) in the north, the natural iron-bearing balls found in the Veluwe and the red iron ore near the rivers in Brabant. Smiths travelled from small settlement to settlement with bronze and iron, fabricating tools on demand, including axes, knives, pins, arrowheads and swords. Some evidence even suggests the making of Damascus steel swords using an advanced method of forging that combined the flexibility of iron with the strength of steel.

In Oss, a grave dating from around 500 BCE was found in a burial mound 52 metres wide (and thus the largest of its kind in western Europe). Dubbed the "king's grave" (Vorstengraf (Oss)), it contained extraordinary objects, including an iron sword with an inlay of gold and coral.

In the centuries just before the arrival of the Romans, northern areas formerly occupied by the Elp culture emerged as the probably Germanic Harpstedt culture while the southern parts were influenced by the Hallstatt culture and assimilated into the Celtic La Tène culture. The contemporary southern and western migration of Germanic groups and the northern expansion of the Hallstatt culture drew these peoples into each other's sphere of influence. This is consistent with Caesar's account of the Rhine forming the boundary between Celtic and Germanic tribes.