Old Greek lacking craft to make crossing (4)
I believe the answer is:
span
'crossing' is the definition.
'old greek lacking craft' is the wordplay.
'old greek' becomes 'spartan' (I've seen this before).
'lacking' is a deletion indicator.
'craft' becomes 'art' (I've seen this before).
'spartan' with 'art' taken away is 'SPAN'.
'to make' is the link.
(Other definitions for span that I've seen before include "Extent - 9 inches" , "Extent of aircraft's wing" , "Ox team; bridge" , "too short for the foot" , "Distance between bridge abutments" .)