Final answer:
The most outstanding achievements of the Byzantine rulers include their advanced diplomacy, the splendor and economic prosperity of Constantinople, and the cultural development during the Macedonian Renaissance.
Step-by-step explanation:
The most outstanding achievement of the Byzantine rulers can arguably be attributed to their innovations in diplomacy, the rich and glorious splendor of Constantinople, and significant contributions to cultural and religious development during their rule, such as the Macedonian Renaissance.
Byzantine diplomacy was renowned for its effectiveness, particularly through the establishment of the "Bureau of Barbarians", which specialized in gathering intelligence on rivals and preparing diplomats for missions.
This approach to foreign policy and intelligence included underhand tactics and strategic alliances that maintained Byzantine influence. Additionally, the splendor of Constantinople, with its vast size, wealth, and beauty, played a major part in the success of Orthodox conversion among Slavic peoples.
The magnificence of Constantinople included impregnable defensive fortifications, a cash economy, and a lucrative silk industry, becoming a bedrock for wealth generation within the Empire.
Lastly, the cultural achievements of the Macedonian Renaissance represented a period wherein the Byzantine Empire experienced an artistic and scholarly revival that would later influence Italian art and the Italian Renaissance. These emperors pushed back against military threats, fostered stability, and promoted cultural innovation during their rule.