Some walls and monuments are still lying there today in what we call Dublin Castle. Dublin Castle lies in the very heart of Dublin. It stands on the highest ground in the locality which has something to do with strategy. Because of its location the people could see enemies at long distances and alert the others. In fact we saw the walls the vikings made in the Undercroft next to the Cork Hill Gate, when we visited the site. In 1014 the Irish army under the command of King Brian Boru won the fortress back, but the vikings were allowed to stay at the fortress as long as they paid tribute to the Irish. The vikings actually stayed in Dublin for another 160 years until both the vikings and the Irish were defeated by the Normans in 1169. The vikings were ejected and the Normans became the next occupiers of Dublin. The Normans strengthened and expanded the existing town walls.
On the 30th August 1204, King John of England started the erection of a larger and stronger castle. It was made with strong walls and good ditches for the defence of the city. The construction of Dublin Castle was completed in 1230. After that Dublin sustained economic growth for a while, and the population may have reached 10,000. But the Norman townspeople and the Irish clans were in constant fight. That cost a lot of the castle's treasury, and that was evident when Edward the Bruce, brother of Robert, King of Scotland, landed with his army in 1315, to set the United Celtic Kingdom. Joining with many Irish Chieftains he took over the castle. They de-molished a number of buildings and used the stones to strengthen the town de-fences. .
In 1348 a far more deadly enemy stroke Dublin. The Bubonic Plague also known as the "Black Death" hit the town. At that time Dublin had suburbs that were not sur-rounded by city walls. People inside the walls thought that the plague came from the outside so the city gates were closed. That was a terrible mistake, because rats spread the plague inside and coursed even more infection and death.