The site chosen to erect the fortress consists of a collection of granitic rocks restlessly rough-hewed by stonemasons. In this regard, the place name «Rocha Forte» (Strong Rock) pays homage to a type of enclosure, build on rocks, which is widely found in the northwest of the Iberian Peninsula. The recent archaeological excavations have brought to light the marks indicating where stone should be cut and they tell us of the impressive undertaking of flattening the stone to erect the physical and symbolic core of this military enclosure: the keep. Erected at the highest point, the place with the best view, this keep was among the most monumental in the Galicia of the time.
The work of the nameless stonemasons who built and extended the fortress between the 13th and 14th centuries has survived in the marks on the rock and on the bond stones. The excavations have also provided us with remains of the tools used to cut and work the stone like wedges and chisels. Due to the humidity and acidity of the soil, only stone and iron tools have survived (and very poorly so). But among the tools used some were made of wood and many of the structures of the castle have not survived because they were made of perishable materials.
After the Irmandiños destroyed it, stonemasons returned to the ruins of the old castle. The archbishop decided to reuse the bond stones and take them to the castle at Pico Sacro . This removal of stone was supervised by the master stonemason of the cathedral, who did a good job as the plundering was systematic. The only bond stones that have survived were those beneath the ground at the time. This plundering meant that by early 17th century there were few remains left at surface level. In May 1617, stonemasons Gaspar de Arce and Francisco Gómez Araúxo, and carpenters Xoán Varela and Afonso de Beade visited «a place by the name of A Rocha, where a tower is said to have risen» in order to make an on-site assessment of the feasibility of rebuilding the fortress.