What is the grammatical role of the "lay" in the following sentence? It seems like a verb. But why it is not used like a third person form (lays) or "lay" is the past form of it?

> 
> First, attention may be given to the doctrine of geographic causation.
>  It stresses the decisive importance of the location on Moscow for the
>  later expansion of the Muscovite state (the medieval state centered in
>  Moscow) and includes several lines of argument. **Moscow lay as a
>  crossing of three roads**. The most important was the way from the
>  historically crucial city of Kiev and the declining south to the
>  growing northeast.
> 
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