Herodotus's accounts of Persia cannot be trusted in their particulars, yet historians cannot do their work without relying on him because the Persians themselves left almost no narrative histories.
Historian Lloyd Llewellyn-Jones argues that Herodotus's histories are riddled with fantasy and fiction, yet remain indispensable since the Persians left no comparable written record of their own.
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Lloyd Llewellyn-Jones: We cannot believe much of what Herodotus says, and yet we cannot do without him. Some historical truths about the Persians may well lie hidden in Herodotus, but one needs to dig deep through the layers of fantasy and fiction to find them.