Police called off an area near a reservoir after a suspected Second World War Two bomb was discovered on Friday morning.
Dyfed-Powys Police said an Explosive Ordnance Disposal team were called to the Cantref Reservoir in the Brecon Beacons.
The A470 near Nant Ddu Lodge and A470/A4059 junction, which was closed as a precaution, reopened shortly before 1pm.
Dyfed-Powys Police said: "Thank you for your patience while we dealt with the incident".
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