is considered to; it is said that ~
とされる indicates a general or widespread belief or assumption, equivalent to 'is considered to' or 'it is said that'.
とされる is the passive form of とする, which itself means 'to regard as' or 'to assume'. When used as とされる, it shifts the focus to the fact that something is generally regarded or believed by people, often based on research, tradition, or common knowledge. It is commonly used in news, academic writing, and formal discussions, less so in casual conversation. The nuance is that the speaker is reporting a prevailing view without necessarily endorsing it personally.