The using of the principale towers was for protect the angles of the enclosure, in a more exposed position than the frontal parts, regarding the fact that it couldn't opposed the enemy only a small number of defenders.
The towers are sometimes vertical, sometimes take the shape of a frustum of a cone; often these two formes combined, rising a vertical fortification on a conical foundation or in pyramidal form.
There are towers open in interior, but usually, don't overtop the height of the enclosure walls and aren't in this case, frankly speaking, only prominences of the fortifications. This disposition was adapted beyond all doubt because, through a minimum expense were obtained the majority of the advantages which offered the usual towers. However, the closed towers had always a more general utilisation, and were, frankly speaking, fit as being more powerful than the preceding ones.