Tiberius died on 16 March 37, and Caligula became Emperor. He accomplished this with the aid of Praetorian prefect Macro and the consuls of 37 who agreed to nullify Tiberius' will, thereby allowing him to inherit all of the estates which otherwise would have been divided with Gemellus. Gemellus was formally granted his "toga virilis" (toga of manhood), was adopted by Caligula, co-opted into the Arval Brethren, and given the title of "princeps iuventutis" (leader of the youth). His "tirocinium", the public ceremony where young men donned the toga and became eligible for military service, was held in July 37, and a "congiarium" of 75 denarii was distributed to each citizen by Caligula. Comments by Tacitus and Suetonius that he was still a child this year, despite the fact that he was 18, may refer to his mental development. This would explain why he had not yet received the toga of manhood.