The present study sheds light on a rare type of Rasulid dinars, namely the coins of Sultan El Mu'ayyad Da'ud, which were the first to represent the type and to imitate the Hafsid dinars that are distinguished by their square-in-circle design. The present study tackles various issues in an attempt to explain this phenomenon. The first issue concerns the reasons that led to the appearance of this type of square-in-circle Rasulid dinars for the first time in the Sultanate of Sultan El Mu'ayyad Da'ud. The second issue concerns clarifying the reasons why the examples of this type of coins were restricted only to Aden's mint. The third issue focuses on why this type of dinars reached Yemen. In order for the study to reach conclusions, the researcher adopts an analytical approach that relies on induction and on analyzing what historians and modern authors wrote, as well as on examining examples of the coins that resembled the type of Sultan El Mu'ayyad Da'ud's coins in the world coinage catalogues and coinage auctions. The present study, which relies on analyzing and discussing the issues mentioned, reached certain conclusions, the most important of which is that the square-in-circle design type of coins imitated the types of Marinid and Hafsid dinars which represented the square type. The study also postulates that this type of Sultan El Mu'ayyad Da'ud's square-in-circle dinars are referred to as Royal Dinars in historical sources, and they were not issued until 720 AH/1320 CE, in El Mu'ayyad Da'ud's Sultanate. They were also issued in Aden's mint, which is proved as the striking of this type of square-in-circle coinage continued in Aden's mint in the Sultanate of Al-Mujahid Sayf al-Islam Ali, son of Sultan El Mu'ayyad Da'ud.