And, 'at last,' we can see the outer surface of the tent. If the pictures inside allowed us a voyage back in time in the preceding years, the objects outside make us travel backwards in time for centuries - a couple of millenniums, approximately - up to the Trojan War.
It is not only a poetical device, for Tasso, to say that those lances would "hardly be carried" by Achilles, Ulysses, etc. In fact, he followed the already ancient Greek opinion according to which humankind is getting weaker and weaker. A view still defended e.g. by the Italian poet and scholar Giacomo Leopardi in the early 19th century. As an 'actual' example of this, Tasso adds in Gerusalemme Conquistata a character who didn't exist in the Liberata: Giovanni (John), a some 300 years old warrior who has taken part in the wars of Charlemagne, meeting the Emperor himself as well as Paladin Roland, etc. Sort of a Highlander like in the 1986 movie. This also creates a link between Tasso's poem, set in the late 11th century, and the Carolingian Cycle, about 800 AD, therefore 'invading the turf' of his direct competitor, Ludovico Ariosto's long poem Orlando Furioso.