Herod introduced numerous architectural innovations and construction techniques in his buildings, such as the domes inside the Double Gate to the Temple Mount. He adapted the mikveh — a Jewish ritual bath — for use as the frigidarium in the Roman-style bathhouses in his many palaces. Herod also developed an innovative combination of palace and fortress; examples include the Antonia Fortress in Jerusalem and the Herodium in the Judean Desert about 2 miles south of Bethlehem. Characteristically, they have (or had) one tower higher and stronger than the others. Herod’s fortification innovations strongly influenced the military architecture of subsequent generations.