The present note studies a sufficient condition that the length of the $3$-class field tower of a cyclic cubic field is greater than $1$.
"A note on the $3$-class field tower of a cyclic cubic field." Proc. Japan Acad. Ser. A Math. Sci. 83 (2) 14 - 15, March 2007. https://doi.org/10.3792/pjaa.83.14