When the centrally organised Foreign Ministry of the Habsburg Empire was created in 1720, there were 19 diplomatic missions, of which the oldest one was in Constantinople established in 1547.
Furthermore, it needs to be highlighted that before World War II there was a division between embassies and legations based on the system of diplomatic ranks established by the Congress of Vienna of 1815.
Until the mid-20th century, most diplomatic representations were still legations as embassies were reserved for a few of the major world powers or close allies.
As the name indicates a Minister also had plenipotentiary powers (i.e. full authority to represent the head of state), but was ranking below an Ambassador.
The title of ambassador had been used before the Congress of Vienna by the Habsburg Empire, but all relations at ambassadorial level, whether permanent or temporary, were downgraded in 1849 following the revolution.