Research at Rujm el-Hiri, a Bronze Age megalithic monument in the southern Levant, provides a broad insight into two episodes in the prehistory of the Levant---the construction and usage of the Early Bronze Age (EBA) ceremonial complex, and the erection of a cairn at the center of the monument some 1500 years later. Excavations in 1988--1991 provide information on Rujm el-Hiri's geometry, alignment associations between the architecture of the complex and celestial bodies and events, physical elements in the landscape, and local ecology-related phenomena. We also examine the significance of timekeeping and its implications for the agricultural calendar and cosmological domains of the local cultures. Data drawn from archaeological, astronomical, ethnohistorical, and biblical sources reveal the sophistication of the 3rd millennium B.C. construction phase of the Rujm el-Hiri complex. Among the finds reported are the systematic use of a measuring unit to construct the site; the establishment of an accurate alignment system for both celestial and non-celestial elements in the landscape; the organization of an orientation calendar as a basis for economic activities; and the hints of a rich cosmology. Overall, our study of the Rujm el-Hiri megalithic phenomena reveals a level of cultural complexity not previously documented in the Levant of the 3rd millennium B.C.