Complex sentence: Today only marshes are left next of Aghios Panteleimonos beach marking the original swampy wetlands, which used to cover 100 m. by 1 km.8 to 10 km² before drainage somewhere in the late 2nd millennium.
Split into simpler sentences: Today only marshes are left next of Aghios Panteleimonos beach marking the original swampy wetlands. Only 100m by 1 km.8 to 10 km² used to cover before drainage somewhere in the late 2nd millennium.