How many letters does the top answer for “a city of central china; capital of ancient chinese empire 221-206 bc” have?

The most common answer is sian (4 letters).

Crossword clue: a city of central china; capital of ancient chinese empire 221-206 bc

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

sian 4 letters wn-def

a city of central China; capital of ancient Chinese empire 221-206 BC

xian 4 letters wn-def

a city of central China; capital of ancient Chinese empire 221-206 BC