The castle's remnants date back to the 15th century. The fortress was a huge square flanked by big towers. Guingamp city was born in the 9th century; when the Normans besieged it, count of Avaugour built a strong castle in order to protect his lands.
Then, lords of Penthièvre built a fortress and surrounded the city with vast walls. In 1340, Guingamp was confronted to the Brittany's War of Succession; the city supported Charles de Blois, so the Montfort allied with the English besieged it. Those one won the war and demolished city's fortifications, in 1420.
When duke Jean V gave Guingamp castle to his son, the fortress and its walls were rebuilt. During the war of Religion, the city supported the duke de Mercoeur; cardinal de Richelieu was very upset of that, so he ordered the demolition of the castle in 1626...