The volume The Tori: The Grand Fishing Activity in the Middle Ages in Lake Trasimeno (by Ermanno Gambini and Elio Pasquali, translated by Roshini Mallah) is a unique source in English on the topic of “tori” (tower) fishing on Lake Trasimeno in the medieval and early modern periods. Guerra Edizioni, 1996. A detailed text and a number of watercolors explains the method of fishing used for centuries. For the sake of brevity, though, we’ll quote the short description from a guidebook written by one of the same authors on the lake:
“This fishing system, not in use for over four centuries, is unknown to our modern fishermen. There is however abundant documentation from the eleventh to the sixteenth centuries, a testimony of the economic value of an undertaking that was managed at the time like a large firm when Lake Trasimeno was seen, first by the City of Perugia and then by the Papal States, as a precious good to take advantage of, but also to protect. The preparations involved not only the fishermen but a good part of the lake community during the annual cycle.
In the winter the woodsmen cut the trunks and poles of chestnut or oak that were necessary for the final phase of the fishing. In the late spring everyone was involved in bringing down from the forests the enormous quantities of oak branches used to make thousands of bundles that then, in summer when the lake was calm, were transported with boats to be sunk in preselected locations, where the stacks from the year before were. Hundreds of pyramidal piles were constructed – these were the tori – where the fish found refuge from the rigors of the winter. The fishermen cultivated hemp on the banks of the lake, from which they made the nets, in particular the huge one used in “tori fishing,” called the travencule.
The fishermen dedicated to this technique of fishing (which netted mainly tenches, but also nases and eels) were organized in “Companies.” Each Company was composed of nine men: a head boatman (called a navarca) and eight workers, and a large boat (called a nave) and a small helper boat (called a navigiuolo) were used. In the middle of the fifteenth century there were forty Companies; each one had between fifty and sixty towers. In the summer and the winter the lake teemed with men and boats in feverish activity. Matteo dall’Isola Maggiore [a sixteenth-century humanist and island resident], in the second book of his work the Trasimenide (1537), describes the epic deeds of the fishermen of his age, doing this same fishing technique at the height of the winter, in inclement weather conditions, with the tools of the trade that had assumed cyclopean dimensions because of the high level of the lake.
The fishing community of the Isola Maggiore shook themselves awake from sleep three or four hours prior to dawn. After having consumed a frugal breakfast, the men loaded the boats with the tools needed for that day’s fishing. The large ships left port with their small helper boats (the navigiuolo) in tow. The fleet went out together for a bit, then broke down and each crew headed for the toro selected for that day’s fishing. As soon as the light levels permitted it, the crew chief or navarca got on the navigiuolo and took the precise coordinates (local landmarks) for finding the submerged toro ; this was called l’istra or il listro in local jargon. Having found the toro, the navarca called the crew him: the fishing could begin.
The crew began right away to build around the submerged tower two circular structures composed of long poles driven deep into the slimy lake bed. The diameter of the external
“palisade” was about twenty-five or twenty-six meters. Four or five meters divided the first palisade from the one inside it. Tightly-woven nets, nine meters high and about eighty meters long, were hung out of the water on the inside of the poles of the external circuit of the palisade. These nets were then dropped down to the bottom of the lake and tied to the inside circuit of poles with ropes. The toro was thereby completely enclosed by nets with all the fish inside.
The crew, part on the larger boat and part on the smaller boat, with hooked rods and long curved rakes, pulled out all the bundles from the water and threw them over the nets to the outside of the palisade. Some of the men stuck the heavy, sixteen-toothed rakes into the slimy bottom to drive the fish who had taken refuge there out of the mud. Others hung some of the bundles of branches into the water inside the nets so that the fish would group around them to hide. This first phase of the fishing ended halfway through the morning. The men came out of the palisade using the helper boat and went back to dry land to have their meal. The fishing started back up in the afternoon.
The fishermen, who had gone back into the central space inside the palisade, used throw nets to try to catch the fish that had remained where the tower had been before. Lined up part on the helper boat and part on the ship, they turned towards the inner palisade. They pulled the ropes in rapidly, raising out of the water the submerged strip of net which they hung on the hooks where before had been the cords. In this way they made a large bed of nets with a circular form inside of which were all the fish. At this point the bulrush knots were untied and the main ship

A detail from the book The Tori showing the fishing from above.
went into the space between the two palisades. From the stern the men began pulling in the net, unhooking it from both sides while from the navigiulo the other men pulled out of the water the half-submerged bundles. Doing this they made the fish gather in a space that was ever smaller.
In the end the fish were carefully dumped into a sack made of netting, called the mutilo, which was then left in the water, tied well to the main ship. The men then pulled all of the poles out of the water. Only the pile of bundles was left behind – they became the base of next year’s tower.The fishermen went to the shore of the lake – it was now almost sundown. They dumped the fish into large braided wicker baskets immersed in water, called bacai, where they left the fish until they were delivered to market.”
(from Isola Maggiore: Historic-Artistic Guide (by Ermanno Gambini and Mirko Santanicchia, translated by Zachary Nowak, published by the Pro Loco Isola Maggiore in 2007)