
1) Briton ruler 2) Celtic boy name
Found on
https://www.crosswordclues.com/clue/cassivellaunus

Cassivellaunus was a historical British chieftain who led the defence against Julius Caesar`s second expedition to Britain in 54 BC. He led an alliance of tribes against Roman forces, but eventually surrendered after his location was revealed to Caesar by defeated Britons. Cassivellaunus made an impact on the British consciousness. He appears in ....
Found on
http://en.wikipedia.org/wiki/Cassivellaunus

powerful British chieftain who was defeated by Julius Caesar during his second raiding expedition into Britain (54 ).
Found on
http://www.britannica.com/eb/a-z/c/33

Cassivellaunus was a British King, ruling north of the Thames, who offered a valiant defence to Julius Caesar during his second invasion of 54 BC. However, he was forced to capitulate and promised to pay a yearly tribute to Caesar and provide hostages.
Found on
http://www.probertencyclopaedia.com/browse/CXC.HTM
No exact match found.