Gauls:
https://www.thesun.co.uk/news/15416021/ufo-dogfights-france-probe-pentagon-aliens/
Belgae:
https://en.wikipedia.org/wiki/Black_triangle_(UFO) Black triangle (UFO) - Wikipedia The Belgian UFO wave began in November 1989. The events of 29 November were documented by over thirty different groups of witnesses, and three separate groups of police officers. All of the reports related a large object flying at low altitude. The craft was of a flat, triangular shape, with lights underneath.
Britoni:
The Rendalsham AFB incident is already fairly famous.
Gauls, Belgae, Britoni...
We need to throw in some Marcomanni, Cherusci, and Quadi episodes.
There are also thousands of reports from military bases all over Mexico, Central and South America - I don’t have any links.