A pinnacle is an architectural ornament originally forming the cap or crown of a buttress or small turret, but afterwards used on parapets at the corners of towers and in many other situations.The pinnacle looks like a small spire.It was mainly used in Gothic architecture.The pinnacle had two purposes:1  Ornamental – adding to the loftiness and verticity of the structure.he pinnacle looks like a small spire. It was mainly used in Gothic architecture. The pinnacle had two purposes: 1  Ornamental – adding to the loftiness and verticity of the structure.