What omen caused Tanaquil to predict that Tarquinius would become king?

Tanaquil predicted that Tarquinius would become king based on the omen involving an eagle stealing his hat. In Roman tradition, this specific event held significant meaning. Tanaquil interpreted the eagle's action as a sign of divine favor and a foreshadowing of Tarquinius's future rise to power. Eagles were often seen as messengers of the gods, and such an omen indicated that Tarquinius would attain a high status, ultimately leading to his kingship. This interpretation aligns with the cultural practices of the time, where omens and signs from nature were taken seriously and often influenced political and personal decisions.