Complex sentence: The 1st Cavalry Division, ordered to hold at all cost the ground between the Somme and the Ancre, saw hard fighting around Sailly Laurette that the 11th were pulled back across the Somme to hold the line at Hamel to block the German advance on Amiens.
Split into simpler sentences: The 1st Cavalry Division was ordered to hold at all cost the ground between the Somme and the Ancre and saw hard fighting around Sailly Laurette. The 11th were pulled back across the Somme to hold the line at Hamel to block the German advance on Amiens.