Like the Double Tower, the semi-lunar tower is a flanking or "on the wall tower".
The purpose of these towers was to make the sectioning of the wall easier and so contain the attackers who got onto it. Because the tower rose well above wall level, it could defend the adjacent wall-walk and act as a lookout and signalling post.
The tower is vaulted at both the first floor level and at battlement level, with no connecting stairs. The tower probably dates from the 13th century but was substantially altered towards the end of the medieval period to accommodate artillery.
During the mid-sixteenth century the Spanish observer, Ortiz, noted that Waterford was surrounded by stone walls with seventeen towers with cannon on them. However, in response to fears of a Spanish invasion, earthen outworks were constructed outside the walls with a view to making them more secure.
These ran from the Beach Tower to the French Tower and appear to have been poorly built. It is likely that the citizens were not serious about the task, as many would have supported catholic Spain at this time.
