I'm reading the passage about the Trojan War in Lingua Latina per se Illustrata: Roma Aeterna (Ch. 37).
The verbs are mostly in past forms (imperf., perf. or plup.), but in line 140~142:
Aenēās vērō, ... atque dēfēnsōribus sēsē adiungit.
the verb adiungit is in pres. form. Is there any reason for it?
(I find the following sentences also have present verbs)
It's called the historical present, and its typically used to make the action more vivid. See Allen and Greenough §469.
The present in lively narrative is often used for the Historical Perfect.
Affertur nūntius Syrācūsās; curritur ad praetōrium; Cleomenēs in pūblico esse nōn audet; inclūditsē domī. (Verr. 5.92)
The news is brought to Syracuse; they run to headquarters; Cleomenes does not venture to be abroad; he shuts himself up at home.
See also this thread on the topic: tense fluctuation in Latin narrative
