Ten mice scurrying around old land of the Aztecs (6)
I believe the answer is:
mexico
'land of the aztecs' is the definition.
(I've seen this before)
'ten mice scurrying around old' is the wordplay.
'ten' becomes 'X' (Roman numeral).
'scurrying around' indicates an anagram.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'x'+'mice'='xmice'
'xmice' anagrammed gives 'mexic'.
'mexic'+'o'='MEXICO'
(Other definitions for mexico that I've seen before include "North American country" , "Country bordering the United States" , "Country of the Aztecs" , "Republic in North America" , "Country south of US" .)