This is the "Dipping Bridge" in the small village of Merthyr Mawr.
The Bridge was first built in the 15th century, or at least Merthyr Mawr House was.
The reason this is called the dipping bridge is simple. Wales has always had many sheep farms. The small arched holes in the bridge were where farmers pushed the sheep through into the River Ogmore for their annual dipping. I would guess, and hope, that the river would be a little higher than in these photographs.
Growing up in the valleys of South Wales, a few miles from here, I well remember farmers, on horseback rounding up sheep from the mountains and hills and driving them through local rivers a few times a year. Of course these days farmers are required to carry out more formal "dipping" using a formulation of insecticide and fungicide to protect the sheep much more effective at removing parasites than this river dipping could hope to achieve.