Since when were European railways considered narrow gauge? The track width was and is standard gauge. The loading gauge was greater than that in the UK.
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1435 mm to be exact. The only narrow gauge track were local lines. Spain and Portugal has even wider gauge, 1668 mm.
The trackwide of the famous Sherman was made to fit just over the 1435 mm. So it was able to use railroadbridges without an problem.