In this paper we suggest an approach for understanding the spatial behavior and structure of cities.' It views cities as physical objects and is based on urban morphology alone. The units of examination are urban clusters instead of municipalities defined by politically determined boundaries. Clusters are defined as contiguous built-up urban areas. We present characteristics of clusters, including their morphology. Previous work that analyzed urban clusters focused on the Pareto distribution of clusters and on the behavior of the biggest cluster. Our work presents a more thorough description of the characteristics of urban clusters. By means of historic data of the Tel Aviv metropolis we present cluster statistics and we study their dynamics. We present characteristics of the clusters from 1935 to 2000, including their number, rank-size distribution, and morphology through the area - perimeter relation. These indicators present important anomalies in 1964 and 1985. Our study suggests that the urban cluster approach can be used as a tool to study urban phenomena and we hope that through them we shall be able to investigate economic and social phenomena as well.