。
The lawyers argued the case for hours.
Literal
Lawyers [topic-は] that case [obj-を] many-hours argued.
弁論する is a near-synonym of 討議する ('discuss, deliberate'), but with a slight difference — 弁論する emphasizes formal legal argumentation as in court, while 討議する is general 'discussion.' 弁論 is the same word that appears in 弁論大会 ('debate contest'), the high-school and university speech competitions central to public-speaking culture in Japan.