The architectural and decorative dataset concerning Seuthopolis, the royal capital of the Odrysian Kingdom in the Tundzha Valley (today Bulgaria), remains notably limited, hindering a full appreciation of its original grandeur. This article addresses this gap by presenting newly (re)discovered findings related to the propylon of the royal palace (basileion) within the fortified citadel at the northeastern corner of the city. This represents the first attempt to reconstruct the architectural and decorative features of this significant structure based on material evidence. We also explore a potential connection between Seuthopolis and Samothrace, specifically the influence of the cult of the Great Gods, suggesting that decorative elements of Samothrace may have been replicated at Seuthopolis. In a broader context, this analysis of architectural marbles paves the way for a reassessment of the debated locations of both the royal palace and the temple of the Great Gods in the city. Our study also aims to shed light on the political dynamics between the Odrysian and Macedonian royal families, particularly in the aftermath of Macedonian expansion into Thrace during the 4th century BC. Ultimately, the findings contribute to a deeper understanding of the Macedonian role in the dissemination of North Aegean religious practices and architectural styles in the region.