といわれている is often translated as ‘to be said that (A)’, or ‘it is known that (A)’. Like とされている, it is another construction that links the 格助詞（かくじょし） (case-marking particle) と, with the passive form of another verb, to mark a commonly held/public opinion. The verb in this case being 言（い）う.
However, unlike とされている which expresses a ‘result’, といわれている expresses 引用（いんよう） a ‘quotation’. To use といわれている, add it to the end of a phrase that you would like to express as being a common thing that is said.

• 大阪（おおさか）のタコ焼（や）きは日本一（にほんいち）美味（おい）しいといわれている。
  It is said that Osaka’s takoyaki is the most delicious in Japan.
• ティフアナは世界一（せかいいち）危険（きけん）な町（まち）といわれている。
  It is said that Tijuana is the most dangerous city in the world.

This particular grammar point is regularly seen both with, and without the kanji for 言（い）う, as the meaning will not change depending on its usage.