I was reading Caesar's De Bello Gallico 1.3.1, and I was curious why he used the word coemere when emere also seemed possible; which got me wondering, what exactly is the difference between the two words?
His rebus adducti et auctoritate Orgetorigis permoti constituerunt ea quae ad proficiscendum pertinerent comparare, iumentorum et carrorum quam maximum numerum coemere, sementes quam maximas facere, ut in itinere copia frumenti suppeteret, cum proximis civitatibus pacem et amicitiam confirmare.
Having been led by these things, and roused by the influence of Orgetorix, they decided to place together those things which pertain to departure, to purchase as great a number as possible of baggage animals and wagons, to do as much planting as possible, so that they would have a supply of grain available on the journey, and to make peace and friendship with the neighboring clans.
I'm reproducing the text (and my translation) to provide some context, and I hope it's helpful instead of distracting. Anyway, I suspect that coemere might be an intensified form of emere, but if this is true then I'm not sure how it intensifies the meaning of the base verb.