The Botan Bridge, built in Siirt Pervari district, was planned to be the country's longest free cantilever bridge before it collapsed. Free cantilevering is a method of construction where a structure is built outward from a fixed point to form a cantilever structure, without temporary support, using staged cast-in-situ construction. The bridge was designed to connect the Southeastern Anatolia to Eastern Anatolia. It has two piers 105.88 m high and the complete length of the deck is 450 m. Prior to the construction of the bridge, a computer model was generated, however there was deviation from the model during the construction without updating the model to reflect the changes. On December 18, 2018, the bridge collapsed during construction without any casualty recorded. Furthermore, it also suffered a partial collapse when the mid-span on the Begendik side fell into the river. The P1 pier was damaged because the parts falling to P1 were hit. Consequently, It was decided that it had to be demolished and rebuilt. This article investigates the actual cause of the collapse with recommendations for future projects.