How would I reword this sentence? "The sacrifices took place at temples, of which the most important was in the ceremonial centre of Tenochtitlan."
This sentence is somewhat awkward because it has prepositional phrases (of which, in the ceremonial centre, and of Tenochtitlan) and two clauses. The simplest way to rewrite it is to try to put the words in an order that makes it easier for our brains to follow.
One way to rewrite the sentence is actually to change it into two simple sentences.
The sacrifices took place at temples. The most important sacrifice was in the ceremonial centre of Tenochtitlan.
You could also say, “the most important of these” instead of “sacrifice.”
If you want to leave this as one sentence, try doing basically the same thing.
The sacrifices took place at temples, and the most important was in the ceremonial centre of Tenochtitlan.
I agree with litteacher8's answer, but if you were really attached to your original word choice, another possible rewrite might be, "The sacrifices took place in various temples, the most important of which was housed in the ceremonial centre of Tenochtitlan." This way, it is still one sentence, it is very similar to your original sentence, but the awkwardness of the second clause is relieved a bit by reordering the prepositional phrases and clearing up any ambiguity of what exactly can be found in the ceremonial center.