When moving from the Mediterranean coast into the hills of Judah (places like Jerusalem and Bethlehem), travelers had several parallel routes to choose from. They were dominated by several valleys in a region called the Shephelah. I want to focus on the three most prominent today.
The first, in the north, is the Aijalon Valley, dominated by the cities of Aijalon and Gezer. There was a road from here that led east up to lower and upper Beth Horon, to Gibeon and beyond. This route is mentioned a couple times with the Israelites routing their enemies westward (Joshua 10:12, 1 Samuel 14:31).
Next is the Sorek Valley. Ekron, Timnah, and Beth Shemesh are important cities here. Samson grew up nearby in Zorah (Judges 13:2) and married a Philistine woman in Timnah (Judges 14). Beth Shemesh is where the Ark of the Covenant was returned from the Philistines (1 Samuel 6).
The Elah Valley is next with the cities of Gath, Azekah, and Socoh. This valley is most famous for being where David fought Goliath (1 Samuel 17).
Why is this important? These were main routes from the hills to the coast and vice-versa. They were like swinging saloon doors that open in either direction. The Philistines lived to the west on the coast while the Israelites (the tribe of Judah specifically) lived in the hills. If the Israelites wanted to get to the coast, they first had to control this region. If the Philistines wanted to come inland, they had to pass through here.
Such is life in border towns. Think about this the next time you read about this region in the Bible.