A town in the Negeb on the southernmost boundary of Judea. Its location is debated, but it's associated with Tell esh-Sharia AKA Tel Sera, Tel Sera', Tell esh-Shari'a, Tell esh-Shari'ah (15 miles southeast of Gaza) or Tell el-Khuweilfeh AKA Tell Halif (10 miles northeast of Beersheba), Asluj a heap of ruins south of Beersheba, and Khirbet Zuheilikah, ruins found on three hills half a mile apart, some seventeen miles north-west of Beersheba.
(https://www.gotquestions.org/Ziklag-in-the-Bible.html, https://www.biblestudytools.com/dictionary/ziklag/, https://www.bibleplaces.com/ziklag/)
When Saul reigned as king, it was under Philistine rule. When David fled to Philistia and lived with Achish the son of Maoch, king of Gath, David asked, "If I have found favor in your eyes, let a place be given me in one of the country towns, that I may dwell there. For why should your servant dwell in the royal city with you?" So that day Achish gave him Ziklag, which belonged to the kings of Judah ever since. (1 Samuel 27:1-7)
David made the town his base of operations for military exploits against the Geshurites, Girzites, and Amalekites, but he reported his raids back to Achish as against the Negeb of Judah, Jerahmeelites, and Kenites. (1 Samuel 27:8-12)
Ziklag burned but its people and possessions restored
When David and his men were sent away from Achish's army against Israel, they returned to Ziklag three days later and found it burned with fire. All the people were taken captive without being killed. (1 Samuel 29:9-11; 30:1-3) David and 400 men pursued and defeated the band, apart from 400 camel riders, and recovered everyone and everything, plus extra - their enemies' flocks and the spoils from the Philistines. David and his men returned to Ziklag. (1 Samuel 30:16-26)
3 days after David returned to Ziklag, a man with clothes torn and dirt on his head came and fell on the ground and paid homage to David, saying he escaped from the Israel camp. David asked how the battle went, and he said the people fell and Saul and Jonathan died. He asked how this man knew, and by chance, he happened to be on Mount Gilboa when he saw Saul leaning on his spear with the chariots and horsemen pursuing closely. Saul called to him and asked who he was. Learning he was an Amalekite, he asked him to kill him. He complied, knowing Saul was close to death. He took Saul's crown and armlet to David.
David and his men mourned and fasted until evening for Saul, Jonathan, and the people of the LORD and the house of Israel. David learned he was the son of a sojourner, an Amalekite. He asked how he did not fear to destroy the LORD's anointed then executed him for his own mouth testified against him.