Rod and line in cart (6)
I believe the answer is:
Here is my best explanation:
'cart' is the definition.
(barrow is a kind of cart)
'rod and line' is the wordplay.
'rod' becomes 'bar' (I've seen this before).
'and' means one lot of letters go next to another.
'line' becomes 'row' (row is a kind of line**).
'in' is the link.
(Other definitions for barrow that I've seen before include "Small cart with two wheels, or old burial mound", "Ancient burial mound", "Small cart with two wheels for carrying things", "Cart; tumulus", "Cart for the river?", "Northern town", "Grave mound - wheeled handcart", "Cart; grave mound", "One-wheeled handcart" and "Cart for carrying small loads".)