Complex sentence: Before the present Junagarh Fort was built, an old stone fort existed here that was built in 1478 by Rao Bika who established the city of Bikaner in 1472.
Split into simpler sentences: Before the present Junagarh Fort was built, an old stone fort existed in the city. This fort was built in 1478 by Rao Bika who established the city of Bikaner in 1472.