Tacitus relates that they were not required to pay tribute to the Romans but were to provide assistance in war and thus were an outpost of Roman rule on the border with Germania. He refers to them in his Germania (ch 29) in relation to the Batavians:
[The Batavians] are not under the contempt of paying tribute, nor subject to be squeezed by the farmers of the revenue. Free from all impositions and payments, and only set apart for the purposes of fighting, they are reserved wholly for the wars, in the same manner as a magazine of weapons and armour. Under the same degree of homage are the nation of the Mattiacians. For such is the might and greatness of the Roman People, as to have carried the awe and esteem of their Empire beyond the Rhine and the ancient boundaries. Thus the Mattiacians, living upon the opposite banks, enjoy a settlement and limits of their own; yet in spirit and inclination are attached to us: in other things resembling the Batavians, save that as they still breathe their original air, still possess their primitive soil, they are thence inspired with superior vigour and keenness.
With the Chatti, the Mattaci took part in the Revolt of the Batavi in 69 AD, besieging the Roman city of Mogontiacum (present-day Mainz).
The Notitia Dignitatum, an early 5th century document, lists two auxilia palatina, the Mattiaci seniores and the Mattiaci iuniores. The references imply Mattiaci in Roman service.