You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Normans

Context:
Opportunistic bands of Normans successfully established a foothold in Southern Italy (the Mezzogiorno). Probably as the result of returning pilgrims' stories, the Normans entered the Mezzogiorno as warriors in 1017 at the latest. In 999, according to Amatus of Montecassino, Norman pilgrims returning from Jerusalem called in at the port of Salerno when a Saracen attack occurred. The Normans fought so valiantly that Prince Guaimar III begged them to stay, but they refused and instead offered to tell others back home of the prince's request. William of Apulia tells that, in 1016, Norman pilgrims to the shrine of the Archangel Michael at Monte Gargano were met by Melus of Bari, a Lombard nobleman and rebel, who persuaded them to return with more warriors to help throw off the Byzantine rule, which they did.

Question:
When did the attack occur in which the Normans impressed Prince Guaimar III occur?

999