but the goths and celts were so far away

[pannous]

Where they? according to the current Theory all branches of PIE came from the northern shores of the Black Sea. given the fact that in those days water ways were the autobahns of their time, this central Homeland was closer to Egypt and Sumeria than it was to France or India. Many Traditions report Skythian origins, surprising how accurate folklore can be.

If you accept Herodotus as a source: He states that beyond the Istros(Danube) lived the Sigynns (probably Zigeuner, (e)gypsies) who had 'Median' customs.
Those Sinti now speak Romani, an Indoarian dialect.

According to Herodotus (chapter Terpsichore) the most populous known nations on earth were the Hindi and Thraker(including Gaetae). The Hindi lived on a subcontinent called India, the Gaetae somewhere in the North, just where a few centuries later the Hindi and Goth appeared, such a coincidence. Also according to Herodotus, the wisest people on Earth (after the Greeks of course!) were the Gaetae. That is quite a compliment considering that he was well acquainted with the Persian, Sumerian and Egyptian philosophers and mathematicians. Long story short: the North Western branch of the Indo European stock seems to have been greatly marginalized by Roman historians for whatever reasons. Maybe you we to adjust our way of thinking about 'Barbarians' as people who said baratha(brother) instead of frater(latin for brother), but were otherwise not that far off science- and technology wise.

In general archaeology provides increasing evidence of an astonishingly connected world early on. (link to Egyptian art in Scandinavian tombs 1x00BC.)