Born in Bucharest, Poenaru attended the local officers’ school from 1859 to 1861, followed by the École supérieure de guerre in Paris.

A second lieutenant from 1861, he rose to captain in 1867 and to major in 1872,[1] and commanded the military engineers’ battalion from 1872 to 1877.

The two continued to collaborate, with Poenaru focused on updating mobilization plans and battle regulations.

He also drew up plans for an eventual occupation of Austro-Hungarian ruled Transylvania, foreseeing a vigorous offensive from multiple directions.

Finally, in the interests of monitoring the border with Austria-Hungary, he detached infantry battalions to the mountain passes of the Carpathians.