Where were the Knights Hospitaller originally headquartered?

The Order of Knights of the Hospital of Saint John of Jerusalem, also known as the Order of Saint John, Order of Hospitallers, Knights Hospitaller, Knights Hospitalier or Hospitallers, was a medieval Catholic military order. It was headquartered in the Kingdom of Jerusalem, on the island of Rhodes, in Malta and St Petersburg.

The Hospitallers arose in the early 11th century, as a group of individuals apparently associated with an Amalfitan hospital in the Muristan district of Jerusalem, dedicated to John the Baptist and founded around 1023 by Gerard Thom to provide care for sick, poor or injured pilgrims coming to the Holy Land.

After the conquest of Jerusalem in 1099 during the First Crusade, the organisation became a religious and military order under its own Papal charter, charged with the care and defence of the Holy Land. Following the conquest of the Holy Land by Islamic forces, the knights operated from Rhodes, over which they were sovereign, and later from Malta.

The knights were weakened in the Protestant Reformation, when rich commanderies of the order in northern Germany and the Netherlands became Protestant and largely separated from the Roman Catholic main stem. The order was disestablished in England, Denmark, Sweden and elsewhere in northern Europe, and it was further damaged by Napoleon's capture of Malta in 1798, following which it became dispersed throughout Europe and Russia.