Archaeological and documentary evidence reveals a complex building history stretching back to the late 12th century. Excavations have uncovered portions of what appears to be an enceinte wall dating to this period, whilst historical records mention a castle gate around 1173 and a bridge with defensive fosse by 1194. These early features suggest that some form of fortification existed on the site well before the more formal castle construction began.

The transformation into a proper castle complex appears to have been mandated by King John in 1204, when he issued orders for the construction of a defensive tower. This directive specified that the tower should serve as the foundation for a more extensive castle and bailey system, a typical Norman approach to establishing military control over conquered territories. The royal mandate marked a significant escalation in Dublin’s defensive architecture, moving from what may have been a simpler fortified enclosure to a more sophisticated castle complex designed to project royal authority.

The incorporation of earlier masonry work into the later castle structure reflects a practical medieval approach to construction, where existing fortifications were often adapted and expanded rather than demolished. This layering of architectural history makes Dublin Castle particularly significant for understanding the evolution of Norman military architecture in Ireland. The site represents not just a single building phase, but centuries of adaptation and modification, from its earliest defensive walls through to the substantial royal fortress that would dominate Dublin’s skyline for centuries to come.