Eorl was given Kingship over Calenardhon for helping Gondor repel an attack from Mordor.

What habit did the people of Rohan practice whenever their line of Kings changed?

i.e. a King dies and has no sons (or sons are dead) to continue the blood line, so a cousin, nephew, etc. is chosen.

Whenever this change of the blood line occurred, the Rohirrim did what?

Hint: It has to do with the bodies of the dead.

I gave the hint because this may be a very difficult one.

EDIT: BLAST YOU TALANTHIAR! Anyway it was Cirion. Answer my question!