Capital I invested in large containers (5)
I believe the answer is:
tunis
'capital' is the definition.
(Tunis is an example)
'i invested in large containers' is the wordplay.
'invested in' means one lot of letters goes inside another.
'large containers' becomes 'tuns' (tun is a kind of container. I am not sure about the 'large' bit.**).
'i' placed within 'tuns' is 'TUNIS'.
Can you help me to learn more?
(Other definitions for tunis that I've seen before include "Mediterranean capital and port" , "North African city" , "N African port" , "North African port and capital" , "Tom, Dick or Harry" .)