Around the time the chancel roof was raised the tower was built at the west end of the nave but  separate from the nave. This is shown by its being built with buttresses at each of the four corners. Towers built integral with a nave have buttresses at the external south-west and north-west sides. The windows are in the same decorated style as the chancel.

On the west wall of the tower above the ground floor window is a niche which once held the statue of a Saint. The probability is that the saint for Harby is the patron saint of the church, St. Mary. Below the niche is a stone in the shape of a shield. The same stone shield is positioned on the north and south walls. The external east wall may have had a shield as well but it is now the west wall of the nave. These shields probably had the coats of arms of prominent  families connected with Harby painted onto them.