The range-finding towers were part of the extensive defensive deployment centred on the four artillery batteries (Amalfi, Pisani, Radaelli and San Marco)constructed to defend Venice against attack from the sea.Those towers are multi-storey structures with a range-finder at the top. This was based on an optical prism system and was used to measure distances quickly. They were built some way from the batteries as their cospicuous structure might help the enemy identify the batteries themselves. They can therefore be found at the side of or behind (particularly along the Pordelio Canal) the batteries which look out over the sea.
From the book: “Edifici storici del Litorale del Cavallino” by G. Bozzato, R. Costantini, P. Santostefano, M. Trevisan, A. Vian.
More about the book: Associazione tra mar e laguna
Mehr about the range-finding towers: www.viadeiforti.it/en