Both “could have been” and “might have been” are grammatically correct, but “might have been” is often preferred in historical or archaeological contexts when discussing a possibility based on evidence. “Might have been” suggests a tentative conclusion, aligning well with the uncertainty often present in historical research. So, the improved sentence would be: “The ancient city found early might have been home to between 30,000 people.” Additionally, you may want to adjust “between 30,000 people” to “up to 30,000 people” or “between 20,000 and 30,000 people” for clarity, depending on the intended meaning.

The sentence should be revised to correct some grammatical issues. Here’s a corrected version for each option: 1. "The ancient city found early could have been home to between 30,000 and 50,000 people." 2. "The ancient city found early might have been home to between 30,000 and 50,000 people." Between requires two numbers to indicate a range (e.g., between 30,000 and 50,000). Which is better: "could have been" or "might have been"? * "Could have been" suggests it was possible for the city to support that many people but isn’t a certainty. * "Might have been" suggests a tentative estimation or hypothesis about the population. Both are grammatically correct, but "might have been" is slightly better for indicating a historical guess or estimation.

'Could have been" or "might have been" would work about equally well. However there are other problems in these sentences: "by found early" makes no sense. Whatever is trying to be communicated here needs to be rephrased. "between" = it is impossible to be between one thing; there must be two things (in this case numbers) for it to make sense: . . . home to between 30,000 and 50,000 people.