Histories

Now if the Babylonians had known beforehand or learned what Cyrus was up to, they would have let the Persians enter the city and have destroyed them utterly; for then they would have shut all the gates that opened on the river and mounted the walls that ran along the river banks, and so caught their enemies in a trap.

But as it was, the Persians took them unawares, and because of the great size of the city (those who dwell there say) those in the outer parts of it were overcome, but the inhabitants of the middle part knew nothing of it; all this time they were dancing and celebrating a holiday which happened to fall then, until they learned the truth only too well.