Following (a) 9) - his victory in 1066, William the Conqueror had a great stone tower built (b) 3) in the south-east corner of London's Roman city walls, serving as an observation post and stronghold (c) 1) against attacks from unruly Londoners and possible invaders. It was a huge edifice (d) for its time. (e)  2) Over the centuries it has functioned as a fortress, a zoo, an arsenal, prison and a museum.

a2 b3 c8 d5 e1