
ANGOLA # 535 (StampWorld.com) issued in 1965. There are four values in the set. This copy is postally used.
The bridge formerly known as the Ponte Doutor Oliveira Salazar in Angola is located in the northern region of the country, crossing the Cuanza River.
The bridge was an engineering project designed to link the central-eastern plateau with the rest of the country. In the post-colonial era, its colonial name was stripped away, and it is simply referred to local residents and transport networks as the
Ponte sobre o Rio Cuanza (Cuanza River Bridge)
It was built as a multi-arch, reinforced concrete bridge consisting of 15 distinct arches resting on hydrodynamic stone pillars, totaling about 308 meters in length. The bridge was damaged during the Angolan Civil War of 1975. It has since been restored to original specifications.
The bridge over the Kwanza River, near the town of Cangandala in the province of Malange, is a multi-arch bridge in reinforced concrete built in 1973 and badly damaged during the conflict in Angola, with six of the arches and one pillar being completely destroyed.
The structure consists of 15 arches of varying lengths that total about 308m between the ends of the abutments, supported on stone pillars endowed with hydrodynamic shapes.
Since it is a structure with great heritage value and that imprints a very strong mark on the local landscape, it was decided to preserve its original configuration and the rehabilitation project involved the reconstruction of the destroyed parts, the integral rehabilitation of the structure, as well as the enlargement of the platform.
The rehabilitation works began in June 2008 and ended in November 2010.
Undated postcard of the bridge from the colonial period front and back


So, from what I could find the set of stamps was issued in 1965, but the bridge was not completed until 1973, damaged in the Civil War and restored in 2010.