The Arsenale (from the Arabic darsina'a or house of industry) is one of the oldest naval dockyards in the world, and was the basis of Venice's great naval power.
It is all the more frustrating, therefore, that is not normally open to the public. Indeed it is still under military administration, and is guarded by men in uniform.
All you can do is go up to the main gates and examine the fine collection of lions (and the men in uniform, if you so wish). The bald one sitting on its haunches is believed to date from 1040 (lion that is), and to have been carved by Viking mercenaries.
The winged St Mark's Lion above the pedestrian entrance, is apparently the only one in Venice shown with the book closed.
Traditionally, the lion was depicted with the book closed when Venice was at war, and with it open when Venice was at peace.
When open the book is inscribed with Venice's motto, Pax tibi, Marce, Evangelista meus (in two columns as Pax - Evan, Tibi - Geli, Mar - Sta, Ce - Meus), which translates as Peace to you, Mark, my Evangelist. That seems a good enough reason to close the book when at war.