Apologies, i wasn't super clear.
Firstly, fleugs I did not contradict myself, you misread.
The earliest physical evidence of marijuana were charred seeds found on a ritual brazier that dated 2500 bc in modern day Romania.
The earliest documented evidence of marijuana comes from much earlier in china, as a medicine and as a textile, and India, as a spiritual aide. (the Bengal people of India are named after Bhang, an Indian variant of prepared cannabis, Bangladesh means "bhang land people")
I did make a mistake in referring to the Mesopotamian empire. What I meant was Mesopotamian Empires and what I was trying to convey by that was the collection of Mesopotamian cultures that existed during the period, ie. Assyria, Babylon, Akkad.
To clarify:
The charred seeds were dated from approx. 2500 bc, a period categorized as the early to mid bronze age. This period witnessed the rise of imperialism in powerful Mesopotamian civilizations, which in turn resulted in a heightened cultural exchange between eastern Europe and the Indian subcontinent, the east and west fringes of the expansive spheres of influence of these empires. The physical evidence in Europe and the written testaments collected from ancient Asian cultures indicates that the first real transcontinental exchange of cannabis most likely happened during this time, most likely via the Assyrian people.
(if you want to know why it's assumed to be the Assyrians it has to do with documents found in Assubanipal's medical library, as well as their cultural association with the Scythians who according to herodutus were the big time European stoners of the ancient age.)
Also, you're right. They didn't have phone lines, or roads. I'm referring to cultural exchanges that happened through trade and migration.