Polydorus is known for supposedly supplementing the 'Great Rhetra' of Sparta. According to the Greek biographer Plutarch (writing roughly 700 years after the Spartan king), Polydorus and his co-king Theopompus changed the constitution of Sparta so that the Kings and the Gerousia (28 chosen men above the age of 60) could veto decisions made by the spartan Apella (the male citizen body).
Classicists and historians find it difficult to fully understand the unique constitution of Sparta due to a lack of sources, so analyzing the reliability of Plutarch on Polydorus is difficult.
Pausanias, another greek writing under Roman rule, gave a detailed account of the first messenian war, a conflict between Sparta and their neighbours who would soon become their slaves. He tells us that Polydorus was in charge of the left side of the Spartan forces at Ampheia, but that his co-king Theopompus was in command of the right flank (more influential for spartan offensive tactics).