There are actually two bridges here, the foreground one made of stone, and in the background (you can barely make out in this frame) made of steel.
"The correct name for bridge in the foreground is 'Stone Bridge of the Main Gate' and the bridge in the background is called 'Steel Bridge of the Main Gate'...'Nijubashi' usually indicates this 'Steel Bridge of the Main Gate'
The stone bridge, with its reflection in the water, is sometimes referred to as a meganebashi style or “spectacles” style bridge because of the arches forming glasses when its reflection meets each end of the arch.
The name "Nijubashi" derives from the fact that in the olden days, this Steel Bridge was made of wood and was further reinforced with wooden beams, thus creating a so-called double bridge.
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