The large scale O.S. maps mark the site of `Oldcastle-upon-Alun' in a small field on the N. side of the farm of that name. The name, correctly Oldcastle-upon-Alun, has been extant in the vicinity since the mid-12th century, surviving unchanged for Oldcastle Down, the high ground N.W. of the site.

The re-use of medieval dressings in the immediate vicinity increases the credibility of a castle or strong house here. These dressings relate to two doorways, respectively of 13th- and 15th-century character.