Inspection shaft at the principal spring of the Convento de Cristo aqueduct, a 16th-century National Monument hydraulic structure at Tomar.
The Nascente do Cano inspection shaft (poço de visitação) is a component of the Aqueduto do Convento de Cristo, also known as the Aqueduto de Pegões, a late-16th-century hydraulic engineering structure at Tomar in the Portuguese Ribatejo. The aqueduct was built from 1593 under the direction of the architect Filipe Terzi to supply water by gravity from four springs to the Convento de Cristo across approximately six kilometres of terrain. The Nascente do Cano is the uppermost of these springs, situated at 153.43 metres altitude.
Water is captured via an underground conduit (mina) discharging into a trapezoidal decantation tank measuring 2.10 metres deep, housed in a stone-built spring chamber with a barrel-vaulted interior. The inspection shaft (poço de visitação) gives access to this underground collection system. The aqueduct has been classified as a National Monument since 1910.
It remains extant, though in varying states of repair along its length, and the spring structures form part of the listed monument.
The Convento de Cristo at Tomar developed from the 12th-century Templar castle and church, evolving into a major conventual complex through successive periods of building under the Order of Christ. By the late 16th century the convent relied on the accumulation of rainwater and had no adequate permanent water supply. When Filipe II of Spain became king of Portugal and, by that role, Master of the Order of Christ, he commissioned Filipe Terzi — architect-in-chief of the kingdom — to design an aqueduct to provide abundant water for the convent and the gardens of the Cerca dos Sete Montes.
Construction began in 1593. A deed of purchase of the spring sources and adjoining pinhal land was executed in 1595. The aqueduct collects water from four springs and carries it by gravity across the parishes of Carregueiros and the União de Freguesias of São João Baptista e Santa Maria dos Olivais. Its most dramatic section crosses the Vale dos Pegões on 58 full-arch spans, with the deepest part resting on 16 pointed arches raised on massive masonry piers — the pegões — reaching a maximum height of approximately 30 metres. A further section crosses the Vale da Felpinheira on 12 round-arch spans reaching about 15 metres at the highest point. In total the structure has 180 arches across its aerial sections. The channel was covered throughout with stone slabs to exclude animals, dust and leaf litter and maintain water quality.
The Nascente do Cano is the principal upstream spring, located at 153.43 metres altitude. Its spring chamber is built in stone with a barrel-vaulted interior and contains the trapezoidal decantation tank and an internal bench of continuous masonry along one lateral wall. Water from three further upstream springs is brought to this point via a half-round-section conduit embedded in the floor, discharging into the decantation tank alongside the flow from the Nascente do Cano itself. A sluice gate permits diversion of flow to the exterior for cleaning. The inspection shaft (poço de visitação) provides access to the underground collection conduit. The aqueduct begins its descent at this point, maintaining a gradient of between 0.2% and 1.5% throughout its length to deliver water by gravity, overcoming a total fall of 26.28 metres from spring to convent.
The channel reached the convent enclosure (cerca) in 1614, initially terminating in an irrigation tank. It was extended to the convent itself by 1617, supplying the monks' wash facilities. The work was formally concluded in 1619 with the construction of the fountain of the Claustro Principal, attributed to Pedro Fernandes Torres.
The aqueduct continued to supply the Cerca Conventual for more than three centuries, until its functional use was abandoned in the 20th century. Two mães d'água — spring-head buildings capped externally by domes and containing vaulted decantation basins — were built at the upstream and downstream ends of the main arcaded section.
The Aqueduto do Convento de Cristo was classified as a National Monument by the Decree of 16 June 1910. A Zona Especial de Proteção was published in 1979. Documented maintenance and restoration works took place at various dates through the 19th and 20th centuries, including 1948–1949 works involving iron access doors, wall and channel rebuilding, and re-laying of sections. Damage was recorded at the Nascente do Cano in 2005 during installation of a water supply pipe. The DGPC geospatially referenced the full aqueduct alignment and its protection zones in 2021, and the Tomar PDM revision of 2009–2021 integrated the full aqueduct trace into the architectural heritage map.
Today the upper sections of the aqueduct, between the springs, are those in the poorest condition, with abandoned agricultural land and vegetation encroachment contributing to decay. The section at the Nascente do Cano and the spring chamber structures remain part of the protected monument.