Qal‘at al-Bahrain is a typ­i­cal tell — an arti­fi­cial mound cre­at­ed by many suc­ces­sive lay­ers of human occu­pa­tion. The stra­ta of the 300 ? 600 m tell tes­ti­fy to con­tin­u­ous human pres­ence from about 2300 BC to the 16th cen­tu­ry AD. About 25% of the site has been exca­vat­ed, reveal­ing struc­tures of dif­fer­ent types: res­i­den­tial, pub­lic, com­mer­cial, reli­gious and mil­i­tary. They tes­ti­fy to the impor­tance of the site, a trad­ing port, over the cen­turies. On the top of the 12 m mound there is the impres­sive Por­tuguese fort, which gave the whole site its name, qal‘a (fort). The site was the cap­i­tal of the Dil­mun, one of the most impor­tant ancient civ­i­liza­tions of the region. It con­tains the rich­est remains inven­to­ried of this civ­i­liza­tion, which was hith­er­to only known from writ­ten Sumer­ian ref­er­ences.