This photo shows the upstream face of the CsI electromagnetic calorimeter. The calorimeter consists of 3100 crystals, each 50 cm (27 radiation lengths) long. The inner crystals have a cross-section of 2.5 cm by 2.5 cm while the outer crystals are 5.0 x 5.0 cm. 80% of the crystals are actually pairs of 25 cm long crystals which have been glued together to form a single unit. The remaining 20% are single crystals. There are two 15 cm by 15 cm holes at the vertical midplane of the detector to allow the two neutral beams to pass through.