Constructed in 1845, Twr Mawr lighthouse (meaning "great tower" in Welsh), on Ynys Llanddwyn on Anglesey, Wales, marks the western entrance to the Menai Strait. In 1975 the function of the Twr Mawr lighthouse was taken over when more modern equipment, showing flashing red and white sector lights, was installed in the nearby smaller tower, the Twr Bach ("Little Tower") lighthouse. [Wikipedia].