Protein synthesis by the ribosome is highly dependent on the ionic conditions in the cellular environment, but the roles of ribosome solvation have remained poorly understood. Moreover, the functions of modifications to ribosomal RNA and ribosomal proteins have also been unclear. Here we present the structure of the Escherichia coli 70S ribosome at 2.4-Å resolution. The structure reveals details of the ribosomal subunit interface that are conserved in all domains of life, and it suggests how solvation contributes to ribosome integrity and function as well as how the conformation of ribosomal protein uS12 aids in mRNA decoding. This structure helps to explain the phylogenetic conservation of key elements of the ribosome, including post-transcriptional and post-translational modifications, and should serve as a basis for future antibiotic development.