This expansion is made of 10 (36 cards total) of the building cards BGGers suggested in this GeekList, and the ones that got most votes went to the Finalist Round.

Keeping in mind the results of the round, the Cambridge Cames Factory employees chose what cards to keep. They were then helped by some BGGers in playtesting/tweaking them and the final results are here.

This Promo expansion was reserved to the Kickstarters supporters of the Black Box Edition, but it's not excluded that there will be wider print runs.
The expansion was printed in two versions, one with Ed Carter's cartooney artwork and the other using Heiko Günther's essential style.

One note on compatibility: The expansion cards created with the original artwork are 63 mm x 88 mm. The 2007 printing of GtR I.V had cards that were 64.5 mm x 89.5 mm. If you sleeve your cards or have a later printing (which is the most common edition of I.V), then the promo cards will work fine. If not, you will find that the size of the cards is slightly mismatched.

36 promocards:
Bacchanalia (3)
Plebian Council (3)
Watermill (3)
Watch Post (3)
Aerarium (3)
Domus (6)
Triclinium (3)
Castra Praetoria (3)
Castra (6)
Solarium (3): ERRATA IV edition, The card should read: "Whenever you complete a building using Architect, you may move one material from that building into your stockpile. This also applies to Solarium"