ultro

Ultro is an adverb from the same stem as ultra, "beyond", and the spatial sense survives only in the fixed phrase ultro citroque, "there and back, to and fro". Everywhere else it is figurative.

Two senses that look unrelated but are not. First, doing something unprompted, going beyond what was asked: ultro auxilium ferre. Second, and this is the one that trips people, a note of indignant surprise, "on top of that, and what is more", when someone not only fails to do what was owed but goes further in the wrong direction. Livy uses it constantly of an enemy who was not merely defensive but attacked first. Sponte and ultro overlap in the first sense; sponte says the will was internal, ultro says the action exceeded expectation.