The project was created with plaster of Paris blocks cast in-house and glued together with simple white glue. Then undercoated and drybrushed. The structure has been used extensively in various demo games of Games Workshop's Lord of the Rings line
I built the Gate of Minas Tirith with Jaroslaw Grabowski of WargamingZone and BuyPainted fame who is also the author and the producer of the moulds.