The history of the Jews in Croatia dates back to at least the 3rd century, although little is known of the community until the 10th and 15th centuries. According to the 1931 census, the community numbered 21,505 members, and it is estimated that on the eve of the Second World War the population was around 25,000 people. Most of the population was murdered during the Holocaust that took place on the territory of the Nazi puppet state called the Independent State of Croatia. After the war, half of the survivors chose to settle in Israel, while an estimated 2,500 members continued to live in Croatia. According to the 2011 census, there were 509 Jews living in Croatia, but that number is believed to exclude those born of mixed marriages or those married to non-Jews. More than 80 percent of the Zagreb Jewish Community were thought to fall in those two categories. Today, Croatia is home to eight synagogues and associated organizations, located in Zagreb, Rijeka, Osijek, Split, Dubrovnik, Čakovec, Daruvar, Slavonski Brod. Of these, the Zagreb community is the largest and most active, organizing events such as the annual Zagreb Jewish Film Festival to promote Jewish culture and identity. Jewish traders and merchants first arrived in what is now northern Croatia in the first centuries of the Common Era, when Roman law allowed free movement throughout the Empire. Archaeological excavations in Osijek reveal a synagogue dating to the 3rd century AD, and an excavation in Solin discovered Jewish graves from the same period. A Jewish community in Split was found to have also emerged in the 3rd century. In the 7th century Jews sought refuge in Diocletian's Palace after the Dalmatian capital Salona was overrun by the Avars. A synagogue was built into the western wall of the palace in the 16th century, and descendants of the Salona refugees are still living in the area. One of the oldest written sources, which could indicate the presence of Jews on Croatian territory, comes from the letter of the vizier Hasdai ibn Shaprut, which was sent to King Joseph of the Khazars.