The Bruceterian seeress
Veleda was a Bructerian seeress who played a significant role in the Batavian revolt.
The word Veleda seems to be a title: it may be a Latin rendering of the Celtic word Veleta, 'seeress '. The Veleda we know about, predicted the successes of the Batavians when they revolted against the Roman empire (69). It is not known whether she merely prophesied, or actively incited the rebellion.

In March 70, the predicted successes became realities: the Batavian leader Julius Civilis captured the legionary base at Vetera. The commander of the Roman garrison, Munius Lupercus, was sent to Veleda. When describing this incident, the Roman historian Tacitus explained who she was:
Veleda was an unmarried woman who enjoyed wide influence over the tribe of the Bructeri. The Germans traditionally regard many of the female sex as prophetic, and indeed, by an excess of superstition, as divine. This was a case in point. Veleda's prestige stood high, for she had foretold the German successes and the extermination of the legions.
Munius Lupercus never became her slave: he was killed on his way to Veleda. We do not know why. A few months later, the Batavians captured the flagship of the Roman navy, which they proceeded to tow up the river Lippe to present it to the prophetess, who lived in a large tower near the river.

Authority
It is certain that Veleda had great authority. For example, it is known that the inhabitants of the Roman city Cologne accepted her arbitration in a conflict with the Tencteri, a tribe in 'free' Germany.
After the suppression of the Batavian revolt, the Romans captured Vedela (or offered asylum to her). This happened in 77. She is said to have served the Roman interests by negotiating with hostile Germans. It is not known to what incident(s) this refers, but it may be noted that in 83 or 84, the Romans forced the Bructeri to accept a new, pro-Roman king.
A Greek epigram found at Ardea (a few kilometers south of Rome) ridiculizes Vedela's prophetic talents. It has been said that this epigram suggests that Ardea was her place of detention. However, this is far from certain. Vedela was not the only German seeress known to the Romans. Tacitus informs us about a colleague.
They even believe that the female sex has a certain sanctity and prescience, and they do not despise their counsels, or make light of their answers. In [the emperor] Vespasian's days we saw Veleda, long regarded by many as a divinity. In former times, too, they venerated Aurinia, and many other women, but not with servile flatteries, or with sham deification.