US bought Louisiana from the French for $15 million. I read over the internet that some people say it was cheap. I thought $15 million at the time was expensive? I googled how much the price would be today adjusting to today's inflation and it is worth $225 million. Am I wrong to think $15 million was expensive in the 1800's?

Edit: Wording

Considering they traded regularly with each other was there any cultural exchanges or embassies established?

Nowadays, American prisons seem generally designed to punish criminals while keeping them separate from the general population. Was this always the case?

We celebrate the 10th year more than almost any other in anniversaries. The 30th birthday is objectively very similar to the 29th or 31st, but viewed as a "big one." It's crazy to think that our numbering system has actually impacted how we celebrate as a society.

Do we know of civilizations that used base-12 number systems celebrate 6, 12, and 144 as more special holidays? What years were the "big ones" in ancient cultures, and why? (I'm specifically interested in "Eastern" and "Roman" history, but I'll love anything you know)

After the fall of the Western Roman Empire, the population of Rome shrunk drastically, and afaik it took centuries until it regained its original population and geographical sprawl. When did the "modern" Rome become as large as the ancient one?

Were slaves treated differently in California and the say Colorado and how were they treated by their owners or other miners in the area.

To my understanding, the standard Pre-Marian battle formation consisted of a layered system in which Hastati engaged first, followed by Principes who would fill in the gaps, and finally Triarii if the shit hit the fan. Cavalry would be kept on the extreme flanks, and a thin line of velites and leves would launch pila before any infantry engagement. That being said, when the Marian reforms occurred, standardization of equipment became a big aspect of that. With that however you lost the layers of experience. So what would the Romans have done as a standard pre-battle formation after that?