I read a book regarding the kings of Sparta, Killings in Sparta (Omoruri in Sparta), by Kostas Assimakopoulos, about two of the most known rulers of this city, Agis IV and Kleomenes III. Since you are from Romania, I think that you will be able to fiind this book in the old book-shops if you are interested. The year of publication is 1983, at the Univers Publishing House.