Covenants are unique as Arts and generic as Enhancements - Cities are the same, unique as Forts and generic as Sites. So you can only have 1 of the Fort but multiples of the Site. Or one of each.
That's true for all dual icon cards that aren't generic or unique as both types - you can have 2 Babylons but only 1 The Harlot, for example.
REG 5.1 was uploaded to Cactus and LoR yesterday, and that's covered in the Unique Card and Generic Card entries in the Glossary.
